Two things that make auction's work.  Some people don't know the actual "street price" on items, (could be anything) and "I gotta win the prize" attitude.

All it takes is 1 who doesn't know the relative price and 1 "gotta win" attitude and you're gonna see some silly A_ _  prices paid for stuff.

If it were me,, I'd search the machinery sites for 5-8 comparable machines, average out the prices on all of them. Preview the machine(s) your interested in before the auction. Before the bidding starts put the paper with the average price in 1 hand, and your bid card in the other, keep looking at the average price paper in your one hand as you bid with your other hand, but if/when the bid price exceeds your known "street price", stop bidding and walk away. 

NO I'M not saying or advocating being a shill in any way, just do NOT let "bidder's fever" kill off your common sense or shoot yourself in the wallet either !!

I've seen great stuff practically stolen at auctions,, and I've seen krap sell for as much as Brand new.  All depends on the bidders and the "want/gotta have factor".

O' the last factor(s) ??   Weather and time of year, Cold n' nasty outside,, The bidder's are either there to buy period at any cost,(very serious buyers)  the "it'd be nice to have" guys won't show. If the auction is during a busy time,, won't be as many bidders either.

(I'll probably get hate mail from auctioneers for years..   )