I have puchased from Ebay and have been happy with the goods and price. Like anything, you need to go carefully - as allready mentioned check out feedback, check the items bought and sold by the ebayer to give you an idea of how they got their feedback. Check the dates of their prvious transactions. Check thier location.You can mail them a question.
Lots of sellers have ebay shops and. or links to a website where you can get more details about them. This all helps to get a picture of the seller. I know that this is involved but it can save you hassle and save money.
I would advise reseaching the price of whatever item you are after - look at amazon as a guide and then seach for the best deal online. When you find a supplier you are happy with, search for any voucher codes for extra money off - it only takes a minute but can save you significant amounts of money.
The above is not a recomendation from me and you shop entirely at your own risk!