I dont think there is any chance of stopping it.
It can only happen by leaving a bid of which you just have to take it on the chin
Its a case of go to the auction,bid live on the internet /phone ,use a dealer or as i have a forum member.
Most auctions you can bid live (as in the above) so i dont see any reason to leave a bid and how do you know you were not bid up.
Yes you may ask someone to go to your maximum and not get it as your maximum was matched but atleast you know exactly.
If you leave a bid and dont get it.......its only a coin.