Wealthy Elven Bards and the Bow of Infinite Money

[Gnaskar]

I'm running a rules as written dungeon fantasy campaign (after 10 years of far too many inconsistently enforced house-rules, it felt like it was time for one where we use the rules in the books and only those). During yesterday's char gen session, an interesting loop hole was found:

Elves lop 10% of the final price of "Elven" gear, buying such gear for 90% of listed price. Bards have a decent chance of being able to sell items at 100%, especially if this is what they're specialized in. First a reaction roll with a host of bonuses, and if that fails, a high merchant skill. Then luck.

So what's stopping an elven bard from buying an Elven Shortbow at $765 and then selling it at the shop next door for $850? And, with a little bit more seed capital, doing the same with an Elven Composite Bow (earning $1,530 in the process)?

Obviously, it can, should, and probably will be rule zero'ed, but that's not the point of this exercise.