All Model iPhone's: Anti Theft Prevention

Hi,

So as the title says really, does anyone have any advice on how to prevent fraud when selling an iPhone or any model device for that matter? for example, does anyone know of anything you could buy to mark a logic board so if a buyer says it isn’t working, upon receiving the item, you can inspect it to see if it was yours? Stuff around those lines. I’m new to phone repairs and I’m just trying to figure out ways to cover my own back and I’d like to know what others do to keep themselves safe for selling on refurbished phones, tablets etc.

Hope this make sense? lol.

Thanks people,

Craig.