I've been paying with my phone for a while and assume it's secure enough. If someone nicks my credit card they could do tap payments more easily. I never buy expensive phones so the old ones are worth bugger all. I do wonder how dodgy CrimeConverters are. I've not bought much from them, but there are so many 2nd hand phones out there. What you got actually seems okay, but I'm surprised you didn't check the paperwork.