Scubamarli pretty much nails it. I'd add that you can now get a Paypal Credit Card and there is suppose to be greater buyer protection using that. I know with either the buyer can issue a fraud claim but I don't know of any way the buyer can retrieve those funds once they're issued. I have purchased and sold several hundred things over the years through Ebay. I've been ripped off once (too good to be true, no feedback but it was low dollar). As big a problem as being ripped off is...ie no product delivered when you purchase, there are other problems of stuff that is way overhyped (as-new etc) or doesn't work when you receive it or damaged. Typically the seller feigns ignorance about the condition of the item. "I'm selling this for my sister's husband's brother and don't know anything about it". Overall, Ebay has been a good conduit as long as you use some common sense as both a buyer and seller.
1. Use your paypal credit card, or other credit card to make paypal purchases. There's greater protection for larger ticket items should a seller scam you.
2. Only ship to places with reputable shippers that insure products.
3. Sometimes too-good-to-be-true is just that, other times you get a Cobra dive computer and Scuba pro G550, MK20 and R390 octo all for $300 (My best deal to date).
4. Your best deals will always be "newly listed" and under "buy it now". People just wanting to get a little cash for something they had lying around a couple of years.
5. Beware of the bait and switch. Some people show photos of items not included in the "listing". They'll usually include this photo to entice unsuspecting bidders to overpay for the items. To protect themselves, they usually have in fine print "only items listed in the description are included".
6. If you're a seller, always stay in contact with your buyer. There's nothing worse as a buyer than shelling out $200 and not hearing from the seller for a week. This also gives the buyer a sense of comfort and affords the seller more leeway from the buyer.
7. If you're a buyer, (most risk in my opinion) and you want to make big ticket purchases the Paypal credit card only protects you up to so much. Check to make sure the Seller feedback is good. If there's no, or little feedback, the item will be cheaper but your risk is higher.
Tip - search ebay items within 100miles and you might find a great deal you can pick up..ie inspect before you buy.