A domain registrar rents domains to individuals (including companies as individuals). At least for the common standard registrars/top-level-domains the rented domain is owned with a guarantee of being able to extend it.

Like with any possession, how it is sold depends the owner.

Where did you find it and where would you “press add to cart”? If it’s a trustworthy platform, the following process depends on them, but for such a high cost I would expect a manual contracted process instead of an automated one.