A shop is a location (usually a building) that sells specific goods. Shops can be found in any non-abondoned city or village. Each shop has its specific good, which is represented by a sign post with a specific image. Shops are usually used to sell items that have been processed from raw material. Shops usually maintain a stock rotation, which means they rotate their stock every 5-10 minutes. Each shop has 2-3 different rotation sets.
Since a shop can be proven to be less-rewarding than player trade, a handy guide such as viGilante's Oberin trading values table can be provided-and checked in the Forum, in order to not waste the most gold, there. Since shops conduct all business in gp, they often are a sink for richer players' wealth, other than Guild Hall things and other necessary and sufficient-to-their enjoyment interactions with GMs on rare occasion. Players stock variety.