In my experience of credit card / Mail order fraud (14 years). Things to look for are:
1) Is it too good to be true - People are greedy and want to believe that it is true so overlook the obvious
2) Lack of product knowledge - not knowing what they are selling / buying - although there maybe some genuine reasons for this.
3) Person - Over the last 14 years 98% of our attempted fraud has been from people with an african dialect (when we have spoken to them on the phone). Although using ebay doesn't facilitate phone conversations, look for mispelling of obvious words and bad grammar. A classic is people even getting their name the wrong way round and trying to sound english. In some countries the surname is first following by the first name. So they would use Williams John as a made up name for example. If you get the opportunity to talk to them engage in conversation and all should become clear.
4) Try and ask for a phone number and then check the person on BT's directory enquiries. Say that you need to ask then some technical details and can talk them through how to find them on the engine over the phone for example. If they phone you then see if they withhold their number.
REMEMBER: Decent people don't mind giving details - fraudsters always have something to hide.
Credit Card fraud (like auction fraud) is soooo easy it is frightening, we had one person who was doing it at the same address for 4 years! - Police were notified in 2001 and arrests made finally in 2005. The police only took action as there were so many cases that it was affecting their figures!!
As there is no way of a merchant reporting a suspect or fraudulent card transaction to the bank in the Uk (Yes that is correct!) fraud is rife. I'm sure a large percentage of ebay goods are stolen / fraudulent goods be resold.
IMHO I would not trust ebay at all - they may have tightened up their procedures but like the bank they have no real incentive to sort out the problem.
These people may help http://www.reportauctionfraud.co.uk/
- its a new site but for a couple of quid it may help you - NOTE: if the person isn't on the list it doesn't mean they are genuine - just not a KNOWN frauster.
Hope this helps.