Exactly. What I do unless I'm not going to be here when the auction ends. Then I just bid, like you say, the maximum amount I'm willing to pay.
What amazes a lot of us is how close to new prices some people will pay for used parts.
I won an auction for a gear drive recently but, it got bid up to exactly $400.00 within the last few minutes. Not a few odd dollars or cents over like most snipers would do so, I suspect the owner was making sure he got at least that amount for it.