I am one of the product testers mumsnet chose for the weight watchers product trial. As a part of the trial we had to sign up online and provide payment details. We were promised that no payments would be taken but that they couldn't change the system to avoid providing the details.
I used my paypal account and after the first month was charger the full months membership. I checked the feedback thread and saw that this had happened to lots of us.
We were promised that it wouldn't happen again, and wanting to believe the best in people I left it at that thinking is was a genuine mistake which was now rectified.
The product test ended in December and I along with lots of others have been charged again. As soon as people started reporting it in the feedback thread MNHQ closed the thread. I sent them a Pm and started a thread asking what was happening. replied that they were dealing with it so I didn't complain I waited for my refund. Annoyingly it goes back onto my paypal balance so takes me bloody ages to actually get my money.