After getting to HMV for the first time and trying to sell all the loot from two vaults in UD, I have exhausted all the money that Leggot had.
The result was this somewhat funny chain of messages:

Leggot mumbles: "Sorry, but I ain't got the money to pay you." You see Leggot
happily ringing the cash box bell.
Leggot mumbles: "Sorry, but I ain't got the money to pay you." You see Leggot
counting money.

How can he count the money if he doesn't have any? What's the ringing of the cash box for when it's empty?

I guess either increase available gold that shopkeepers initially have, to allow the players to sell all they have for sale or completely suppress the above messages while the shopkeeper is out of cash.