Not always.

If you use a snipe guard it has to be made known there is one upon creating your auction, you can't choose to add one when your auction is almost finished.

Plus snipe guards only can be used if the winning bid was made in the very last minute before the auction ended. If the winning bid was made two minutes before the auction ended, the snipe guard is voided and that bid is the winner of the auction.

Snipe guards can't go on forever though, and you have to be very specific in how long it would last(ex: 30 minutes) and after that set amount of time has finished the auction is done and can't be extended or lengthened again by any means