I do bit of buying and selling on the side but it's usually only when a bargain comes up, so maybe one every few months if that.

All I do is, register the car in my name and leave it on the drive while doing any work needing doing. If I get someone ringing up to view it, I'll stick a weekends insurance on it for £35 so they can test drive it etc

I keep a record of all costs/profit involved but all sales are cash based and since the car is registered in my name it's technically a private sale

I will go into trading on a more permanent basis, at which point I'll do everything properly but for now I don't see the need