Yep, there have been a few posts about this - one extensive, but as the search function is AWOL, it's hard to find.
Basically: If you do a lot of gift payment, PP don't like it, so they may restrict your account, asking for ID clarification etc.
There are also issues with sending/receiving large amounts (like £4k+ p/a), which require ID certification to fall within EU money laundering regulation.
That's the gist.
What I do is simply pay the %age if someone requests gift.