Here you'll find tips and advices on how to use eBay in a safe and secure way.
The main, and most used, way to check if the seller is a trusted person is the "Feedback".
The Feedback represents the seller, and buyer, permanent reputation as an eBay member. It’s made up of comments and ratings left by other eBay members you've made business with. The overall Feedback Score is available in your, or seller if this is the case, Feedback Profile.
Usually a high Feedback Score is a good sign, but you should always check your trading partner's Feedback Profile to read comments and look for negative remarks. Remember, almost every seller has, at least, one negative Feedback point. Although it is possible they are not actual problems but comments from vindictive buyers. This way, pay attention to any replies the seller may add to the negative point. Most of the times professional sellers will stick to the facts when writing feedback. Possibly shady sellers will add name-calling and such while ignoring the facts.
The following links may help you with aditional information.