How to buy safe Clash of Clans acc?

[Luminary]

I bought the other day CoC acc, not code transfer, he gimme complete google acc, luckily i paid cheaply, but the one who sold it to me still logging into it, so i dont want to repeat mistake again, question is, how to buy safely CoC, when one trader sells it can not be anyone but me logged in!


sry for my not so perfect english!

ty