It will not be advisable to make transactions in bitcoin within a country where cryptocurrency transactions are illegal by the law. But Imagine this scenario that someone has been using their bitcoins for transaction secretly successfully, and then one day decides to use the bitcoin that they have to make payment for something like a property to the owner of the property, If there is this kind of problem for instance where the owner of the property decides to claim that they did not receive any money in bitcoin, and the case is taken to a law court, what do you think the outcome of the case will be?
If proofs of payment are provided but in cryptocurrency, do you think the court will consider it even though transactions are tagged illegal with it? or will the case be thrown out and the owner of the property with the false claim of not receiving the money be allowed to go freely?
I don't know people do things these days but i can't pay for a property without a legal binding stating the means of payment, how much to be paid and signature from both parties. When there is a legal binding the need to obey the fact that Bitcoin is not legal for payment will be adhered to. But if they intend on doing it outside of the legal binding then proper video coverage of the transaction should be don't. If the example you gave is a real case scenario the buyer is foolish to have got into an agreement of paying in Bitcoin without any legal binding.
We all know that these days its either people cheating another or fooling the other. Thats why anything we are doing, we should be more careful, taking legal binding and an attorney serious.