I assume that there are limitations on what kind of loot can be sold in markets of a given class. It doesn't make sense to me that the PCs could sell really high-value gems or whatnot in any normal village, or even fairly large towns.
But I can't find anything in the book stating precisely how to deal with this. I expect I just don't know where to look.
So, help me out: How much and what kind of treasure can PCs turn into liquid assets in any given size of community? I assume that if they have thousands of GP that they want to make portable, I can assume there are gems available according to the guidelines on the chart in the Equipment chapter.