I agree with both you and parent. People are uncomfortably inconsistent. If a certain rule benefits them then they'll favor it ... right until the rule becomes a problem for
them or favors their adversary. Normally, I see this when people talk about their politics.
On the other hand, Amazon has an unbelievable amount of power. And I think things would be a lot better if we as a society applied the spider-man rule. With great power. If a small mom and pop makes this sort of mistake, then I'm all for them correcting it and not giving away $13K equipment for $100. Maybe they were doing it maliciously, but because of how small they are the scope of their malice can only affect a small number of people. On the other hand, Amazon has the power of a first world nation state. If they make a mistake, innocently or maliciously, then the scope can affect a lot of people. Yeah, you messed up Amazon. Don't export the cost of failure onto people without the power to fight it. Pay for it yourself with your considerable resources and then resolve the issue with your considerable resources such that you don't make the mistake again.
EDIT: Mom and pop might not have the resources to cover their mistake AND they might not have the resources to reasonably prevent it from happening again. And because of their lack of resources they are also on a level playing field with their customers. So if their customers feel that what was done to them was wrong, then they can reasonably challenge mom and pop in court. On the other hand, if Amazon decides that their customers are going to lose in court, then their customers are going to lose in court.