Classic coins is correct , they stopped contact to bidders thru the
ebay system . But it also is true that inexperience collectors started to watch known collectors and other dealers on what they were bidding at . Lets say your a expert on Tibet and you bid on a common Tibet first issue a $20.00 stamp and your bid is $15.00 ,then I know your seeing something that I don't see ,that's when I start to bid against you because there is a reason your buying it .
It is also part of the story that SCADS failed because
ebay and the APS made some kind of screwed up deal for $100,000 to assist in fighting fraud and identifying bad sellers . APS wanted to stick their nose further into the
ebay tent but the higher ups at
ebay close it down .
Another problem was the
ebay Stamp Chat Room started to become a closed group who felt like it was their chat room and you were a outsider walking on their space .
So you can see a lot of different factors were all part of the reason for them to shut down ,it all becomes who you ask .