So firstly, the question was about Covid safe transactions not an ultra safe way of protecting your car from thieves for which there is, ultimately none. On the question of contraventions, yes, I agree, but look, ask the question, do you have a valid licence with no endorsements. Yes they can fib but use your God given judgment - does this person feel right?
Secondly, re accompanied driving entirely your call. CV-19 makes things temporarily not as they were. So, don't advertise your car right now, or make a judgement call on your adherence to CV regs. Not difficult really - make a decision its as simple as that.