... doing quests for them may grant discounts or expanded selections. "Hey, thanks for getting those loan sharks off my back, have a look at the good stuff". The Ratling trader shuffles some items.

Even better, perhaps there could be a few select artifacts that are in the hands of such traders in each game... but you can't be sure which, and they don't actually identify their items to such a detail.

So, supposing that the Rune-Covered Trident were generated as a trader artifact in your game, there would be one trader carrying it... but there would be a heap of others that would have Rune-Covered Tridents. The thing is, if you buy from the wrong one, then when you buy the trident, the runes just kind of rub off, and it turns out that it's really a Painted Wooden Trident, or if you're lucky, a normal metal trident with an ego (say, a Trident of Defense). Each artifact (that can be held by a trader) could have its own description of what happens when you buy a fake.

To counter the risk of buying a fake, the trader price for the artifact could be somewhat lower than it would be if sold in a shop. Also, perhaps there could be a skill that would increase the chance of identifying it as a fake prior to purchase - say, Appraising. That said, even at skill level 100 (or JADE's equivalent), the chance of identifying a fake would only be somewhere around 40-50%, and it would never actually identify as "the real deal".

@Aielyn - EXACTLY! Say it's marked as "rust covered weapon" and until you identify it, you won't know if you got something that costed you a ton but is worthless, or if you bought something awesome!

All of this! :)