Micky: Yes, I live in Canada.

Try Googling "legal caveat" or "property caveat".

This web site:
https://answers.yahoo.com/question/i...9010855AAIR8H4
explains what property caveats are.

Essentially, just in the same way that a lien against a house means that the house can't be sold without the lien holder being paid first out of the proceeds of the sale, a caveat informs the Land Titles Office that someone else has some form of interest in the house (or other property), and that it can't be sold without permission from a court.

So, if someone who took one of those $300 gift certificates ever wanted to sell their house, they'd have to get the Court's permission, and that Court would undoubtedly rule that the house can't be sold without the realtor's permission or, according to the agreement, without the realtor acting as the real estate agent in the sale. Alternatively, the court might see this as a "scam" and rule that those gift card agreements are unenforceable. But, on the surface it appears to be a legal agreement.

PS:
Both Canada and the USA (and Australia and New Zealand), as former British colonies, inherited the same "Common Law" system from Britain, so there should be the same kind of thing as a caveat in the USA, and it's probably called something very similar. In France, and in former French colonies, including the Province of Quebec in Canada, the law is based on the French "Civil Code". And both the British Common Law and the French Civil Code evolved from Roman Law as ordered to be written down by the Emperor Justinian I so that the Roman Law would survive even if the Roman Empire collapsed. The influence of Roman Law in both British and French legal systems is evidenced by the use of Latin phrases for legal principles. The same Latin phrases that we used today were used in early Roman courts.

Roman law - Wikipedia, the free encyclopedia