The auctions actually get a great amount of exposure - For example, this recent stone had 184 unique views in the one week it was active.
http://www.bonsaiauctions.com/auctiondetails.php?id=684
If sellers set a reserve or a minimum price, there is no reason to be "afraid" of anything. There have been 684 listings and 164 sales, which is approximately a 25% sale rate.
I really don't think we can blame the buyers; it's pretty much up to the sellers to take advantage of the opportunity.
Regards,
Matt