My game is Sigil based. The PCs frequent a magic shop owned by an Arcane/Mercane. It's filled to the brim with dusty magical items leaning against walls, mumified hands stacked with rings, potions bubbling in decanturs, and suits of armor lining the walls. Most items have been there for years, and the lighting is dark and shadowy. A venerable dwarf also works in the establishment, in the back always looking over new magical items and checking weapons.
The Arcane hires adventurers to guard the shop, to find hard to get items, and to make items for him that buyers are interested in. This can spawn adventures or let the PCs get some extra cash through magical item creation. It's always interesting to roleplay the buying because his inventory can change from day to day as he gets new items and sells old ones. One day they might find a nine lives stealer there, the next celestial chain armor.
I think of the Arcane as the ultimate in magical item knowledge. I give them a bardic knowledge type ability and the ability to identify magical items at will. I make up histories for the items on the spot, and the Arcane likes to go on about the item in order to bump up prices (all items from him are +10%-20% depending on item).
He hates buying items since he's already got so much stock, some of it in storage even! But, he'll still buy from loyal customers. Generally he'll buy for half price, but sometimes marks it down even lower if its an item that is highly specialized. Basic items, though, like +1 swords and +1 shields he'll always buy because those sell easy.
He also helps people find people to make items for them and enhance existing items. So if you want to add flaming to your +1 sword, he can point you in the right direction for a price or you can leave the weapon with him and come pick it up in a week or so with the enhancement added in.
He even does trades and store credit! The ultimate businessman.
Azalnubizar said:
...I believe no spellcaster would actually spend XP on items for the sole reason of making profit.
A PC in my campaign made a magical item, spending 500 xp, for pure profit.