I heard a rumor once, and I have no idea how true it may be. But the rumor goes something like this: parking lots, beyond being ridiculously lucrative and turn-key businesses, are also fantastic money-laundering or tax-dodging opportunities. And so many of them are owned by shady characters, or shady companies. These types don't necessarily want to deal with things like processing credit cards, or getting into paper trails (although some modern parking lots are using credit card readers, for convenience's sake).

This sounds pretty fanciful, but it doesn't seem entirely implausible.

Occam's Razor says that the garage managers weren't interested because they're doing just fine, and your service wasn't solving a greater problem than the inconvenience of manually dealing with bids would cause. But I wonder if there's another factor at play here. :)

Anyhow, this is a great recap of your approach, and I'm sure it's been a fantastic learning experience for you both. Thanks for writing this, and for sharing it! On another level, it frustrates me to read your story: it seems like you guys had identified a real problem with users ready to try it out, and the other side of the market just didn't have the same degree of need. That sucks.