yes of course details disappear after the transaction on a phone that hasn't been tampered with. you could easily be using an app that pretends to do the work but is actually storing the details to be used later for other purchases.
so someone lets you wander round there home, totally trusts you, quite often leaves money, cheque books / cards, valuables all round the house which we could easily half inch. then they turn round and say, "oh no! i'm not paying you by card, you could use my details later when i'm not there".
what about everyone else that takes cards, local garage, local kebab house, couldn't they do the same. or is it just carpet cleaners that are the scum of the earth and extremely stupid, cos lets face it. this type of crime would be easily trackable.