1) I'm sad to find your totally reasonable comment downvoted. Decline in HN standards, etc...
2) An alternative scenario: what if a car dealership simply mis-priced a car? They're holding a rare race car but the owner asked his know-nothing nephew to appraise it, who was busy texting his girlfriend and absent-mindedly wrote down $500. If you buy this car and the owner realizes his mistake the next day, can he ask for the car back?
It seems the situation is basically if a mistake is made that still seems reasonable (pricing a car for $19000 instead of $20000), it must be honored. If the mistake is completely unreasonable (pricing a car for $20 instead of $20000) it does not have to be honored. But a mistake in business knowledge (pricing a $20000 car for $2000 because you think that's all it's worth) still has to be honored.
2) An alternative scenario: what if a car dealership simply mis-priced a car? They're holding a rare race car but the owner asked his know-nothing nephew to appraise it, who was busy texting his girlfriend and absent-mindedly wrote down $500. If you buy this car and the owner realizes his mistake the next day, can he ask for the car back?