SP probably receive lots of "random" friend request, guys wanting to keep in touch with them and have easy acces to there posting history (to see there ads for exemple)
As for guys receiving request, maybe that person like your reviews a lot, consider you a "person to follow" and consider your opinions and infos.
That totally explain "random" friend requests.
I myself had an SP once sending me one, an SP i saw VERY briefly at one party, never met in private, and who rarely advertise here. I tough it was a bit strange but i was flattered in a way. It mean in some ways she know who i am and noticed me ...
The only strange part about the OP post was the "can't delete them" but if it was a bug of the forum it explain it.