These are great points, but the other issue that I see being overlooked, although it should be considered 'common sense', (seems to be a super power and ultra rare, considering some of the bids I've seen), is how to determine WHAT to bid on a unit.
I personally see what I know is worth X amount, and then I'll add 25% to that, on the assumption that there is that amount buried among the boxes and totes.
How does everyone else do it? (One note that I saw at my last auction, man bid 1,900 to get it, because he saw boxes of what were rims, but they were beat up, and I personally didn't think they had rims in them (they didn't, various hand tools), and he saw what he thought was an antique flintlock rifle. I told him when he was bragging about his 'three thousand dollar antique rifle' that it was a reproduction, because the true old flintlocks used oak, a dark wood, and the one he just bought had a very light wood to it. He got somewhat miffed).
Have at least a general idea of value before you bid. Don't think 'retail' on values, think resale. In this economy, people aren't going to pay you full price with no warranty when they want a bargain. I typically figure 50% of retail depending on the item.