Selling your photos and not getting tricked

I am getting paid to shoot a series of images for a company for which I will send them a cd afterward. Can anyone give me any tips on how to make sure I don't get tricked or taken advantage of?

Should I send thumbnails first until I am paid? Draw up some sort of contract? Anyone have experience in this area?

If you can, get paid before you shoot the event. With that said, I shoot, shoot after shoot after shoot on company's "words". Granted these are magazine companys and news wires like LA times.

If they aren't a reputable company or it's a wedding, try and write into a contract that you are to be paid a deposit to hold a date, then paid in full within a week before that shooting date.

Cheers!