With situations like this I usually allow PCs to sell (or buy) most anything by just saying the following "You're in town for x days/weeks and you manage to unload all of your treaure to various buyers and comission items from various sellers." This prevents the players from thinking their characters are going into the adventurers wal-mart, but it also moves things along.
Of course, if you want to roleplay things a little more, just have the party members make a gather info check DC x to see if they can locate a fence who operates outside the authority of the local theives guild (and then roleplay the encounter) or a guildsman who can be discrete about such transactions (and roleplay the encounter). The exchange should NOT take place in a seedy tavern - too many knowing eyes about. The exchange should take place in a cemetary at midnight, a park at dawn, an upscale eating establishment, under the bridge on the King's Highway, or a drop-site on a certain street corner.