Mr. Walter

A demon merchant concept.

Going by the name Mr. Walter he considers himself a high-class salesman.
Even tho he's clumsy and stupid, he has an affinity for stealing and gathering weird stuff which he will try to sell to whoever he stumbles upon.
Due to his inferior intelligence he can't understand the true value of his items. Thus, the price of an item will be decided based on how much he fancies it.
A useless weird shaped rock may cost a fortune while the luckiest of customers may get rare and powerful magical artifacts at ridiculously low prices.

Nice guy once you get to know him tho.