I have just bought a KT 250 and a Suzuki Beamish from an Ebayer.
The highest bidder had let him down so he emailed me to see if I was still interested. I had to ship my van to the UK and then pick up the bikes. Over a 1000 mile round trip. Well worth it as the bikes were as described and the seller was a great bloke.
I spoke to the seller and his wife and knew that the deal would be OK. Buying from trials riders seems to be alright but you must use your own intuition to get the feel of the deal. Feedback very important, check what the seller has been buying and selling, but voice to voice contact should tell you to be careful or to go ahead. Never go ahead if you are not sure about the deal.
I buy and sell cars, motorcycles and boats on ebay. There are some real scamsters out there. Buyer beware. My feedback is still 100% after 6 years of trading but honesty and good description of the goods goes a long way to help the buyer.