Usually, the store owner will have a contract that outlines their policies, commissions, etc. that you have to sign. Some things you should look for:
Commission fee: Most places charge a commission percentage, the standard here is 30%, but I've heard everything from 10% to 50%. Whatever it is, make sure you're including it in the overhead for your pieces so you're not losing money and it's not too high for the area.
Protection: Some places will insure your pieces against loss (breakage, theft, flooding, etc) and some won't. Find out for sure and what's covered. There's no real excuse not be covered for fire and flood (their insurance company should reimburse them, and they should reimburse you), but theft and breakage aren't always, at least if your piece is the only thing stolen or broken. It's up to you how important this is, but if they don't insure your pieces, ask about theft rates.
Inventory list and tagging: It's a really good idea to have an up-to-date inventory list, with good descriptions and prices, that you both sign. That way, if someone purchases your item, you have a record of it being there and the sale can't get lost in the shuffle.
It's also a good idea to have items that are yours tagged in some way (initials and an item number that corresponds to the inventory on the pricetag are quick and easy) that marks the item as yours. That means the owner can tell which items are yours at a glance and record the transaction accordingly. It's a good idea to ask for these markers back when you get your money so you can reconcile the records yourself. Most shop owners are honest, but mistakes do happen.
