Buyer beware, just like in any other form of trading. However, eBay is biased towards buyers so you have a fair amount of protection if you follow the rules. PayPal offers an extra level of protection and you can also do a chargeback if goods don't arrive or are faulty/ incorrect etc.
When an item that is on offer from many sellers, I go for the sellers with big feedback scores and then look at the negative comments as these are far more telling than the positive ones.
If spending more than around £100, I look for local sellers that will allow item to be picked up and I pay cash. That way I can check item is as advertised before parting with the hard earned.
It may be the area that I deal in (mainly car stuff) but I haven't had any issues buying. Had a couple of chancers try it on when I have been selling (they failed, by the way).
eBay is populated by people so you get the same mix as elsewhere. Most are honest but a few aren't. Most of the dishonest ones are obvious by the listing and feedback. I usually make email contact prior to bidding with a question or two to gauge them.
I would have found doing my car a lot more difficult and expensive if it wasn't for eBay.