At one of these chain restaurants (Olive Garden I think..), I have paid by Gift card which had an opening balance of $50. Our check came to around $47 or so with tax included but not the tips. The gift card was applied and the check was laid out in the usual fashion with a blank line for tips - I left a generous $9 tip (about 20%). I added the check to $56 and signed.

I only later realized that the gift card only had $50 in it… so I guess my balance of $6 tip never got “applied”. I feel sorry for my waiter for being shortchanged because of my error.