Most people will choose to list their complete machines in traditional classified ads format. If you have a machine with limited buyers, then you are willing to wait for 'the right' buyer to come along and pay what's its worth to you. Taking a $2500 machine and starting an auction at $999 wouldn't really work for most people... unless it also allowed a reserve at $2500. This reserve makes it just like the classified ads process anyway.
Perhaps when someone wants to unload a box of parts, or a project machine, or whatever and they really don't care how much they get (low balls ok), then auctions might be fun. But for mainstream pin sales, I think traditional ads with "or best offer" work best.