+1 for Quidco, had over £2300 in 3 years, paid 3 Annual £5 Fees so £15 out £2300 in seems fair to me,
Best cashback was when BestBuy were doing 20% got a Canon 5D MKII Body for £1699 - £340 Cashback tracked and paid.
Some stuff is slow to pay, AA & ther like can take 5 months, but its free money so its just a bonus for when it arrives.
The only reason they would close your account was for pulling scams against the rules (Multiple applications on products that only allow one application), They got hit hard some time ago paying out on Car insurance when the payouts were high and the people cancelled the policy after getting the cashback, so they will come done on those peole who abuse it.
There are always going to be complaints as the payout is never guaranteed and relys on clear tracking (Remember to clear you cache each time you use it or reserve a Broswer just for using Quidco / TCB)
Only non payment I have had in over 3 years, was Vonage, was due £60 but the Middleman went bust and Quidoc did not pay out as they were not paid!. From what I understand TCB did pay out of their own pockets to their customers.
Have a TCB account but never used it ,just find Quidco easy and reliable apart from the one Whoops!!!