You need to cover your own butt when buying stuff off ebay or any forum and don't part with your money till you are fully satisfied that you know what you are getting.
You can ask as many questions, within reason, after you win the auction as long as it's your intention to pay the price you bid when you have ensured the item is as described, that's only fair to the seller.
Be friendly, open and reasonable in your requests to the seller. Most of them are OK and I've never come across one that won't answer a couple of reasonable questions.
When I buy stuff of ebay I get them to answer the question:
Is there any damage or any faults with the xxxxx that you haven't told me about?
I always do this with a bike, frame or set of wheels or large item after I win the auction and before I pay up. If they don't answer then I refuse to pay till they do. If they answer then I pay as soon as I get the reply I'm happy with. This focuses their mind as they want to get the money as quick as possible. It's not illegal and you are well within your rights to ask before you pay regardless of what people may say.
When it turns up take a few photos of the box before opening it, it takes seconds to cover your butt, as they can't pull the damaged in transit stunt if the box is good. If the box is damaged then I make a note on the couriers sheet that it is.
If it's faulty or not as described I insist on them paying the return postage and issue a full refund, If they are from the UK you can do them for misrepresentation and you shouldn't have to be penalised if the item is genuinely damaged or misdescribed when you get it.
Raise the case with paypal and not ebay as paypal has a lot more clout than ebay does, even though they are the same company.
However, there are plenty of genuine and honest people selling stuff and sometimes they are mum and dad clearing the garage, so they get the benefit of the doubt initially, unless they prove to be dickheads trying it on.
There are unfortunately plenty of rip off merchants on ebay and you can spot them easy enough as they are either pushy for payment the instant the auction ends or they get really angry very quickly.
Iv'e had plenty grief for saying this before, but you need to make 110% sure that you are going to receive what you think you've bought. If you need more photographs, get them.
If I'm selling stuff;
If it's broken, damaged or no good I sling it in the bin and don't try to sell it.