I'm a relatively new BeFrugal user... for about a year or so, but I've been using FatWallet, eBates (now the same company), and TopCashBack for about 14 years. Thus far, I've made relatively small purchases via BeFrugal, and have had zero issues.
Recently, however, I made a large purchase from WalMart. BeFrugal had the largest cash back % at the time, so I decided to use them (plus it would put me over my "startup" incentive for bonus cash). Given the order size, I was very careful to ensure I followed the process correctly so I would get this cash back. Long story short, the purchase/cash back was not reported. I opened a ticket, and BeFrugal promptly credited my account, but then came back some time later and said that WalMart had completed an investigation and denied the cash back. Then outlined how I can make my purchases more successful. I responded to customer support to ask for more detail, and they responded with a reiteration that WalMart declined the cash back. I responded again, but they opted to stop responding.
In any event, while they had been OK for smaller purchases, I would STRONGLY advise against trusting them with larger purchases. This may not have been BeFrugal's fault, but bottom line is that something was not connecting right that day, which tells me this is an unreliable service (I'm giving the benefit of the doubt that this was a technical issue and not something more "sinister").