Interesting, however that goes back to my original question about platforms allowing users to create a sub-domain, as they almost always use a wildcard certificate for this purpose. [1]

I suppose the saving grace is that they can only create the _for-sale and not any of the attributes specific to the intent to sell and hopefully that is enough to prevent any shenanigans.

[1] - https://youstareintoconanssoul.ytmnd.com/