I had a demand like that once. I completed a shop and the payment was mailed to me for two shops instead of the one I had done. After waiting 60 days for payment, they noticed the double payment before my check arrived.
The requests for me to confirm that I would destroy the check started with a friendly request on Monday. By Wednesday, I received an e-mail that stated if they didn't hear from me by the end of the day that they would be canceling the check and I would owe the $25 check cancelation fee before they could reissue my check. By Friday, I was notified that I was banned for life because of my fradulent activities. I was geting a minimum of three e-mails a day. The shop plus reimbursement total was $13
There was never an attempt or thought of being fradulent. Hubby and I had gone away for a week to a friend's getaway in Northern Wisconsin. Though they have built a nice home that will eventually be hooked up to utilities as it is where they plan on retiring to at the moment it doesn't have running water or electricity, so of course no internet access either. In preparation for this week, I only did shops the week before that I had done dozens of times in the past with no issues and one shop where I informed the scheduler I wouldn't be able to be reached.
I finally get in touch with this person intent on demanding my pay and they informed me that there had been no action on any of the e-mails, they were just get trying to get my attention. They claimed I was an excellent go to shopper and that they would reissue the check if I would submit a picture of it torn up and I agree to continue shopping with them.
I agreed that I would keep them active. I did get the check two weeks later, but have never done another shop. If they honestly think I am a quality shopper and are willing to get that threatening over a $13 mistake on their end, I don't want to deal with them.