I forgot about an important exception.
If there is a reserve, I guess what I would like it to be. I then bid to somewhere below it. I don't ask sellers for the reserve, because I would feel guilty if I deliberately underbid. If I am told the reserve, I usually go back to ordinary sniping.
I hope that an unknown reserve above the current price will discourage interest and put in a snipe for what I am happy to pay.