Embarrassingly, I fell for the same scam yesterday.
Basically there's a FB post by someone saying they got a box of books from Waterstones after filling out a questionnaire.
Looking back I don't know why I believed it for more than 2 seconds, but it did look convincing - lots of comments on the post from other people saying they'd done it too, with pictures.
Anyway, I did the questionnaire and then went to a payment page where they wanted £4 for the box of books. I started putting my credit card details in, and, belatedly, my common sense started knocking at the door (that old saying "if it looks too good to be true ... "), and I cancelled out BEFORE authoring the transaction.
I then started to receive emails from someone called "underfolders" saying my account was set up, and thank you for my subscription (£51 every 14 days 😲) and got on to my credit card company straight away. They blocked the subscription and cancelled my card so no more payments can be taken. There's a pending payment of some £5 odd, but I should be able to get that cancelled later.
Yeah, I'm embarrassed. I thought I was pretty savvy about scams tbh. But I guess any of us can have a moment of weakness.