Ah it's very simple. First, and just like Issam said, if the auction is too good to
be true, then it's not right. It's dodgy. The auction either gets cancelled or no
one but a noob would fall for it.
To protect yourself on Ebay, look for the following:
1- Make sure the user accepts Paypal (that's the safest way to buy from
ebay) If anything happens, Paypal makes sure the seller refunds your
money.
2- The seller must have at least 99% or in the worst case 98.5% feedback.
3- Read seller feedbacks before you buy, see where do they underperform
and what do they normally sell.
You'll get hoaxed a few times, but it's part of the learning process and
getting to know how to do things properly and correctly. Just make sure
you don't get hoaxed over something expensive.
Happy bidding!