Good Time Charlie's Trading Post is a good place to sell basic loot items.

The West Fudley Market is a good place to get rid of bulk food, drink, clothing and livestock.

There's a chance that the Barons of Bromley or Fudley would buy weaponry, warhorses or luxury goods in moderate amounts (50% chance to buy up to 500gp of such goods). Baron Rufo is less likely to buy such gear (15% chance, but won't spend more than 100gp at a time).

Castle Hydra counts as a Castle for selling loot (see below, at 50% of normal value for gems, jewelry and the like). Hydra company will buy any horses they can at full market value.

You can send almost anything to Marcello to be sold on his next trip to one of the nearby cities. There is, of course a 25% service fee, but he does pay in advance.

You can always make the trip to one of the nearby cities yourself.

There is absolutely no market for herbals in Gerk.

Captured non-magic arms and armor can be sold for 1/3 list price.

Captured silver, masterwork and magic arms and armor can be sold for full list price.

When you have gathered treasure, various items such as gems, books etc., will have a cash value. You may sell them only at a Castle, Town or City. Selling them at a castle will only yield 50% of cash value, a town 75% and a city 100% of the price. The Judge can impose a period of 1d6 days to dispose of loot in a city, while in a town or castle it will only take single day. If you don’t happen to have a Jack or Fighter to appraise things, you’ll only yield 25% of the market price no matter where you sell things.

For these purposes, Critwall and Stoink count as Towns. Radigast, Admunfort and Greyhawk count as cities. Only, Castle Hydra counts as a proper Castle in the Trimarch.