Or do you just allow players to immediately monetize stuff so they can get on with the Dungeon Crawling? Do they sell goods for full retail? How much less?
I've used a simple rule for years now that I think works well. Every member of a given population equals 3 gold pieces worth of wealth that can be obtained by outsiders. So, a village of roughly 1000 people has 3000 gp worth of wealth to dole out. Total. In coins and goods.
This rule is an abstraction, like Hit Points, and it's intended to measure a given locations ability to accommodate travelers. That means if one PC wants to buy a new suit of armor and then another wants to sell the seven emeralds he has they're going to hit a limit quickly if it's a particularly small village. Obviously there are exceptions for some places that are meant to be visited, like an inn along the side of a road, but in general it seems to work quite well and it can end up spurring some interesting role-playing moments as the blacksmith who just took all of a character's coin refuses to buy anything from him. "You just gave me enough gold to retire, why on earth would I spend it on more weapons I would be forced to sell?"