A little history of Flexoffers: I first joined an affiliate site called Cardoffers.com, which will a couple years later turn into Flexoffers. While I was a member of Cardoffers I was pretty satisfied some of their payments would arrive a month or two late, which would put me on edge a little, but for the most part I was pleased with their service.
The major problems began when they switched to the new website. They never said why they switched, but I suspect that the original site was sold, and the new owners didn't want to have anything to do with the affiliate side of the business. The Cardoffers site is still online as a credit card review site.
The final straw for me came when they sent me a check and it bounced. Not only did the check bounce, but the payment itself was three months late. I tried to deposit the check from my affiliate earnings and about a week later the bank told me the account was blocked or frozen. Instead of having $126, I'm out $20 for the bounced check fee.
After that I stopped using Flexoffers, and if you are a currently running their ads I would switch to a different network as soon as possible before you get a bounced check too.