Hey, I'm also new on this message board. I've bought a handful of coins on eBay with mixed results. If the seller does a good job of taking pictures, you may be able to photograde a coin pretty accurately (assuming it's genuine). I bought a common date Walking Liberty half (1942, if I recall) that looked to have terrific luster and strike for about $35 on eBay; I sent it to NGC for grading and it came back MS64, which I was really happy with. I could probably sell it now for twice what I paid.
However, I've had equally bad experiences on eBay, too. I paid almost $20 for a 1943 Mercury dime that looked to have beautiful toning. When I received it, I realized the patina was clearly artificial, as it rubbed off easily between my fingers, revealing a white coin beneath. It still has AU details in my opinion, but nobody wants an altered coin; it was definitely a losing transaction on my end.
Sorry to lead the topic astray a bit; next time I'll start a new thread or find the relevant one to post in. I just think the risks/benefits of buying coins on eBay is really important for those of us just starting out to understand. Glad to be a part of the community!