How much do you consider any of them to be scummy? (from 1=not at all to 5=totally). How would you resolve it?


Gremlin bomb - creating lots of easy to kill gremlins and using them to get easy loot, be it by killing them, or by pickpocketing and then killing them, or having a pet kill them for you (and pickpocketing them). It's not workable for XP since gremlins give few to begin with, and thought they grow more experienced, XP gain is reduced the more often you kill a monster. Note that having items and the knowledge of how to use them are different things.
Scumm-o-meter: 4
Solution: in my opinion, the only thing that have to be changed is the pickpocket skill. It's ok in my opinion to flood a cave with gremlins and kill them; ok, you gain lots of drops, but you also spend a lot of time and after 3k gremlins killed they start to become strong. But it's not ok to spend lot of real life time using that skill and getting lot of great stuff; furthermore it's very unrealistic to pickpocket something that doesn't existed if you kill a monster. So my solution is to change pickpocket making it a skill useful only in new quests, npcs or situations (imagine a level where you have to flee from some really hard enemies). Another possible solution is to add a 1% possibility that a water trap will break when triggered.

ID stairhop - continuously going up and down stairs between two certain ID levels. One could also explore them instead, but stairhopping exposes a maximum of floor tiles per turn. Loot created inside the room is picked up, and accumulates over time. Requires some patience, but is very safe in general, much safer than trying to find the respective loot in-game. Refraining from this technique - or, indeed, from entering the ID at all - will make the early game considerably more challenging.
Scumm-o-meter: 4; this is unrealistic, boring and gives too free stuff.
Possible solution: making every ID level with two stairs up and one stair down; every time you go down, you enter the other level on a stairs that if taken will take you to the level you just explored. The other stair up is in another room (just like the stair down).

Piety overflow - abusing integer overflow to turn big negative piety into big positive and milk your god for goodies. At current time this is considered to be very cheap and exploitish by most ADOM players, but some legit Hall of Fame entries used it. It should be kept in mind that if there was an opportunity in game to achieve integer overflow of experience, it would most certainly defeat the purpose of almost the entire game; this only defeats the purpose of the sub-game of dealing with divine forces and provides virtually unlimited prayers, with all their benefits.
Scumm-o-meter: 3; not game-breaking, just wrong.
Possible solution: I think this is an easy coding matter.

Dragon gold doubling - Dragons which pick up gold drop double the amount drop it in addition to their own gold upon death. Currently there is quite a debate if this is a bug or an intentional feature. Due to its exponential nature, this can easily be used to create truly game-breaking amounts of gold, which are commonly spent on getting piety for precrownings or to pay for Garth's training. There is a bit of risk involved since many types of dragons can destroy entire heaps of gold with their breath attacks, and dragons are relatively rare in the early game and cannot double more than once. Even if the player wants to avoid this effect, it's not always possible to keep dragons from picking up gold in tension rooms or vaults.
Scumm-o-meter: 2; ok, the effect is quite big, but there are risk involved.
Possible solution: maybe raising a little the risk of a dragon brething at the player then dissolving the money.

Stat lowering - intentional lowering of stats by controlled sickness and/or starvation to train stats beyond the common limit of certain methods, such as herbs. Requires some cautiousness. Is not considered to be heavily game-breaking, it only squeezes out a bit more extra stats from a very safe stat training method, and opens up the possibility of being ridiculed for dying of starvation in this manner (even sickness can be deadly, but players will usually have it removed before that happens).
Scumm-o-meter: 1; this is risky and not unbalancing.
Possible solution: -

Wish engine - mostly considered to be to game breaking - once it gets going, the player has basically unlimited wishes at his disposal, which makes the rest of the game about as easy as it can be. The fact that 19 rings can be dipped at once, and a wish for potions of exchange usually returns three potions contribute to the effectiveness of this method. Even 19 wishes, as gained from one successful dip, are more than enough to increase the character's power to game-breaking levels. To gain enough potions of exchange and a stack of 19 identical rings Gremlin bombs are frequently employed.
Scumm-o-meter: 4. Ok, not easy to do, but 19 wishes is game breaking.
Possible solution: making the ring of djinni summoning more unlikely to come out (at the point that an engine is euristically impossible). However, solving the pickpocket skill as I writed before would also solve this problem.

Ring of weakness - easily abused, combined with some potions of exchange and plenty of food and time almost all of your important stats can be increased to 99. Very game-breaking - the player can only die to severe cases of carelessness afterwards.
Scumm-o-meter: 5; 99 to every attribute must not happen.
Possible solution: when wielding a ring of weakness, str goes to 2 and it stops training.

Self education - writing lots of scrolls of education and using them to raise/get some skills. Under certain not really known conditions scrolls can be created without any stat drains, but losing a few points of mana is not unexpected, even with a blessed scroll and writing set. Not that scummy since it does require magical writing sets, rather rare tools, and getting really good skills is not common.
Scumm-o-meter: 1; just a little unrealistic, but interesting feature.
Possible solution: -

Grinding - usually staying on cavernous levels with high monster generation to kill lots of monsters gaining xp, items and weapon skill marks in process. Not very scummy since it is not entirely risk- and hassle-free, depending on the location where you perform it. More dangerous locations will yield greater returns, so for a challenge choose a place where you will be faced with monsters that actually give a fight. Since you will naturally meet monsters and kill them while pursuing your regular goals, such as the overarching quests or exploring dungeons, you often don't have to specifically grind at all.
Scumm-o-meter: 1; time passing = corruption and stronger monsters, so it's ok.
Possible solution: -

Shop restocking - repeatedly buying out all of the items from a shop so that a shopkeeper will produce more items. Can be combined with kick robbing occasionally. Provides a challenge in that obviously you have to get the gold somewhere; of course, gold is not exactly an issue if you use other scumming techniques such as dragon gold doubling.
Scumm-o-meter: 1; it takes game time.
Possible solution: -

Kick robbing - opening a hole in a store wall that allows the PC to kick items out of a shop without enraging the shopkeeper. Most definitely not supposed to be possible, as it usually happens in plain sight of the shopkeeper, and pretty exploitish.
Scumm-o-meter: 2; should be solved because it's unrealistic, but non game breaking at all
Possible solution: making the shopkeeper upset when unpaid stuff goes away from the shop.

Milking - some monsters always, eventually, throw/shoot things at a character which they would not ordinarily drop if they were killed instantly. Allowing them to attack you will ensure you get these items. A common method to stock up on arrows or quarrels, or obtain an orcish spear as early in the game as possible.
Scumm-o-meter: 2; unrealistic but not gamebreaking.
Possible solution: making those monster always drop the stuff they throw when they die.

Pickpocketing - used to gain more items from monsters, as after a certain point about 99% of the creatures you will encounter are weak enough that you can easily afford spending another turn on a Pick pockets attempt. Everything that weighs 10 stones or less can be pickpocketed from any applicable creature, and items pickpocketed will not in any way lower the amount of items you gain from killing - in other words, you will find easily double the (below 10s) items in total, and thus be much more powerful than another player who did not pickpocket at all by sheer availability of resources. There are no good reasons to not pickpocket other than it involves pressing additional buttons (at least two), while most small fry is usually killed in one or two hits. Due to the heavy increase in total loot, a habit some find worthy of picking up, and others can't stomach. The difference is considerable, but nothing which will decide over life and death; a non-pickpocketer will probably simply find himself grinding more often than the pickpocketer.
Scumm-o-meter: 4; boring and quite game breaking.. not to mention it's very unrealistic
Possible solution: making pickpocket steal only stuff that the monster already have (and if not pickpocketed will give when dead).

Banshee in animated forest. One of ways to scum for items is to bring banshee into animated forest. High rate of tree spawning combined with area instakill effect leaves some items rather soon. Although there is danger in banshee gaining some levels and becoming rather dangerous in melee too.
Scumm-o-meter: 1; this is a clever one-time trick and it's ok.
Possible solution: -