Shops are places where items can be bought, and sometimes sold.
You can see pages about shops.
There are a few different types of shops.
These have a very small selection of items to start with, but will buy almost anything from players, and these items are then offered for sale. They will not, however buy stolen items (you need a fence for that) or items that are worth too little.
A general store will not buy anything if it has too many things for sale already.
These have specific sets of things that they sell, and they won't buy anything from players. Items sold in this type of shop usually have labels that can be used to browse or buy them, so that you can "browse a". There are a few different ways these are handled:
These always start with the same items for sale.
These will, at any given time, sell a subset of their full stock. With these, you may need to visit several times if you want something specific.
This usually applies to only some of the stock, not all of it, and can be found in either of the above types. "Uncoverable" means that if you buy a particular item, the next item with that label--or with that type--will be different. So, if item A is a bottle of deep blue ink, and you buy it, A may be a bottle of lilac ink next (with one fewer left).
This is often (though not always) the case with items that are functionally identical or nearly so, but have one or two aspects that vary (such as material, colour, or size), like inks, scented waxes, rivings for woodworking, and charms.
These are shops in which you can order an item to your specifications. It will usually take some time for it to be finished.
These are player-run. The owner decides which items they're willing to sell and how much they'll buy and sell them for. Here, you sell an item, indicate how much you want to sell it for and under what name, and if the owner approves the item, you can come back and collect your royalties. (You can choose to be mudmailed when your items are approved with the syntax "notifications item_approved". The same thing disables these notifications. Notifications are set separately for each shop.)