Many years ago Boots offered phillips c12 mobiles at xmas on buy one get one free offer, I bought quite a few and a week later returned the mobiles for a refund but keeping the free ones, stating they had been given away since they were "free" as pressies. The manager was not very happy, but I pointed out if they had to be returned they could not have been "free" as stated, and we could let TS decide.
I got the refund which was authorised by their HQ but the manager was also told to rip the signs down and finish the promotion, which was helpful since I couldn't compete with the offer at the time