Check the sellers feedback, not all negative feedback is justified, particularly with ebay shops, read the sellers comments. There will always be awkward customers.
Don't shy away from sellers with no feedback, everyone starts with . Contact them, ask something about the item, you should get an idea of how genuine they are from the response. You are protected by Ebay's buyer protection anyway.
Check the bid history, any bids from bidders with  feedback could be signs of shill bidding [pushing the price up]. Any  feedback bidders with a large bid history could be an attempt to mask the shill bid. Again though everyone starts with ,just be cautious.
Don't get caught in a bidding frenzy and pay over the top, someone will probably sell another one.
If you win an item pay promptly, [a] its not fair to keep sellers waiting for their money [b] your item will not be dispatched until you have paid.
Leave Feedback [used by everyone to judge the character of the person they are dealing with].
Enjoy it, its fun, there are some bargains to be had.