However, as a seller I would really like to be able to access some sort of history of a buyer BUT ONLY ONCE THEY HAVE PURCHASED..

Tonal there is a very good reason why that would not work. Sometimes a buyer will find out after they have purchased that there is some reason they should not or cannot pay. If they do not know how to appeal a strike and get it removed it will stay there and then you would be wrongly influenced into thinking they were dodgy. What difference would it make anyway? They still either pay or they don't and you can do nothing you wouldn't do if you did not have the information.