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. As far as I know, the situation does not apply for mis-pricing. Some information here: https://en.wikipedia.org/wiki/Mistake_%28contract_law%29
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.