I love shopping on Ebay when time permits. You can find some good deals, but watch out for the shipping costs. Sometime I'll find a great deal, only to discover that the shipping charges put the cost of the item far above what I would pay at Michaels or Joanns using their frequent 40% or even 50% off coupons. Also, if you are buying books, magazines, or any other publication make sure that these are shipped by "media mail" through the post office. Media mail is CHEAP, although slow, but is sometimes not offered by sellers (and it should be!).
Start out slow. Read the product desciptions carefully. Ask the seller questions if you are not sure. Read the feedback for the seller before you buy. Make sure you understand payment options; some sellers accept personal checks, some only Paypal (you will need to set up an account), some only accept certified funds or money orders (remember to figure the cost of buying these certified funds, as well as the time and gas money spent obtaining them).
My husband sells on Ebay. Books, the odd electronic part, extra cake decorating items, he even sold our piano! I leave that to him and happily spend the money made from Ebay sales on cake decorating items sold on Ebay!