Maybe I'm too skeptical or cynical, but the one time I made an offer on a sealed bid it looked like one hell of a scam. Not a rip-off scam like the Nigerian prince with money he needs help getting, but the type that allows an insider at the auction to magically price their bid high enough to win. Also, it's not always easy to find out who won since it may not be a public bid opening & done in private.
Before the internet, Hemmings Motor News had a big lead time for ads that were a couple of months. The local fire company had an early 50's Dodge Power Wagon that was in nice shape. They advertised it in the legal notices in the newspaper that they were taking sealed bids by a certain date so I went to see it. It was nice, had 6500 miles on it, red & white with a water tank & some other unique equipment mounted.
I turned in a bid on time, & during that same month there was an ad in Hemmings selling an identical early 50's Power Wagon with 6500 miles on it, the same red & white with the same unique equipment for a lot of money & it was right over the state line less than a 30 minute drive. I seriously doubt it was a coincidence that there were two of these trucks with the same miles so close together.
My guess is that someone within the volunteer fire department placed the ad, or had a friend do it & then after the last bid was opened, turned in "the high bid" to win the auction.
