This is a thread better suited for the blackmarket lounge but I'll answer your concern anyway.
If by security you mean the seller charging the pin back, it can always pose a risk. There isn't such thing as a safe pin as they can always be charged back.
However, instead of trying to buy a pin you can try to purchase an RS membership card off someone. I like to buy the cards because it's safer. It can't possibly put your account into negative credit unless it was stolen and you happen to be caught.