Sniping is when you bid at the last minute to undercut the competion. See google, or
http://www.wired.com/news/business/0,1367,55204,00.html
I use ezsniper.com for my own auction bids...works great.
Then there's another issue the car seller should be weary of, shill bidding. That is when someone starts jacking up the price with bids that they don't intend on paying, only to have the 2nd highest bidder come back with 'hey man I'll take it for the price I bid at'. Sellers can also shill bid on their own item to inflate the price.
Anyone selling or buying anything of substantial value on ebay should invest an hour or two to read up on this stuff.