Regarding the
Best Buy gift card bonus: the one time the cashier scanned the QR code BEFORE scanning in the gift card, no "$0 Swagbucks Affiliate" on the receipt so no SBs. Since then I wait till the gift card is rung up, then hand over the printed QR Code and (knock wood!) have not had a problem since!
I don't think they can know for sure if the QR code was accepted until the receipt prints out. By then it's too late and there is nothing they can do.