I've always wondered about that.
I used to buy a lot of stuff for other people that didn't have an eBay account or a credit card.
If they come look at my past buying history, its all over the place and I'd say half of those things were for other people.
Same went for selling items years ago.
I'd sell things for a few friends that didn't do eBay.
I'd have no way to prove otherwise other than that I say it's so.
It wasn't a lot, so probably not on anyone's radar.
It could be a mixed blessing becasue at some point we may need some type of receipt. Online purchases would make that possible. On the other hand I'm sure TPTB have a nice little list of who and what is bought on major gold sites.