If measurements are included, get out a tape measure or ruler to see how big the item will be. If it's for clothes or shoes, compare that measurement to your body. Also, make sure to read the seller's policy on payment and shipping. Find out if they take money orders or personal checks or credit cards. So only bid on things you really want to buy, and follow through with your bid.
E-mail the seller as soon as possible after the auction ends.
Be polite and detailed. Ask how much shipping will be, tell them if you want insurance or express shipping, and ask for the address for where to send payment. E-mail the seller when you put the payment in the mail . This covers your butt and helps the seller know you're serious. Put your payment in the mail no more than three days after the end of the auction.