I played the $14 cashback with booking.com on multiple cashback sites when I was traveling in SE Asia. Most of the rates were pay when you stay. My success rate was less than 50% for getting the payout. Seems they dont like paying out $14 on a $20 a night room.
I still have transactions from booking that are more than a year old that still say pending. When I have contacted tech support for various sites they want me to show proof of the stay, yet they cant even tell me which booking it was for.