This has been answered by many in other sections of the forum, look around please.
What's so hard about cancelling, even WITH a giftcard? Why worry that might get a bill when you can stop that all together and cancel before the trail.
My only concern, and this is where I need your help...is do any of the TOC's that you have read state anywhere that the company can send a bill to your address or attempt to bill you using a method other than the CC you originally used.
I don't think this has been answered anywhere, perhaps it shouldn't be. I have cancelled all offers done on GC, and I can say that there is no hassle even if you cancel after the trial and they have been trying to charge the GC. I think if too many people try to do offers like this, it could be the death of freebie sites, as advertisers will catch on and we will lose our good offers.
But just so we know, can these companies send you a bill in the mail if your card keeps coming back declined?
Can you guess why this was locked?