I write this from experience of buying radio equipment through Ebay in the hope that others may in some way benefit. It is not my intention to teach anyone to "suck eggs" and a lot of what I have to say is common sense, saying that it is easy to get carried away in the heat of the moment.
The average cost for good Ham gear is pretty high and we stand to lose a fair amount if items are not correct.
Due to its very nature of self training etc, there are a lot of licensed hams who tend to modify equipment in one way or another ie broadbanding or increasing power output via some of the modern engineer menus. In some extreme cases you could end up transmitting outside allocated bands.
I purchased a Yaesu 817 (5w qrp rig) that was putting out 14 watts - the guy said he had it from new and it had not been tampered with! How long would those finals last at that output?
Some peoples version of "mint" and "as new" need to be taken with a pinch of salt. Please do not get me wrong, I am not having a go at any sellers but be aware these things do happen.
If you are able to collect and test the equipment before paying that is the best way. In a lot of cases because of distances involved this is not possible. In that case do you know any other Ham operaters in that area who would be willing to go and see it? Most are really helpful. Maybe you could organise a sked to hear the thing working albeit you do not know the equipment being used is what you are going to buy!
If there is a listing for something that seems to good to be true - it probably is! Beware the scammers and 2nd offers from abroad.
Where possible - contact the seller via the "ask seller a question" link - get a phone number and talk to them as to condition, reason for sale etc - you can learn a lot about the seller from a conversation.
Most of the time you will find that Ham operaters are helpful and honest and will not mind in the least answering any questions you have - just do not be caught by the odd few who are selling their equipment because something is wrong and expensive to fix.
It you are a Ham operater my best wishes to you - enjoy one of the most rewarding hobbies in the world!