In common law jurisdictions it'd likely be the courts setting the limits, using judgement and precedent to set what is reasonable and what is not in the contrac

In common law jurisdictions it'd likely be the courts setting the limits, using judgement and precedent to set what is reasonable and what is not in the contract. If they put there that they get your car, and come to collect, you tell them to take a hike, they can sue and likely lose because a judge would say it's unreasonable, and they'll be on hook for court costs. In the borderline cases, may still be worth it for them, but pushing it too far is just losing money.