Future Shop in Ottawa (South Keys) routinely sells items with security tags still attached; these set off alarms when the paying client attempts to leave the store.
It's bad enough to have to deal with all of the usual Future Shop annoyances, from hard-sell tactics to push overpriced and largely-useless "extended warranty" schemes to the sale of "open box special" items at slightly-reduced prices without mentioning that these are often missing key accessories (discs, power cords...)
The abuse of the RFID anti-theft tags, however, is a little more serious. I have no idea what the store stands to gain by doing this, but I've had this Future Shop sell me items with these tags still in place and active twice in the same day. These are not isolated incidents.
Evidently, these folks have an endless collection of excuses. For instance, they may attempt to claim that the offending tags came from "items from some other store" even if you haven't visited any others. They may attempt to grab the paid items and/or the receipts right out of your hands - and in many cases the printed receipt is the only evidence of ownership you have.
Confront them about this, and they blithely reply "well, I gave the items back" seemingly oblivious that grabbing them in the first place is, well, stealing. If a store wants to tag items, they should remove the offending tags BEFORE they take your money - afterward the items are your property so it's a little too late. Future Shop appears not to grasp this simple concept.
Falsely accusing someone is a serious matter and one would expect that sooner or later these folks may just end up on the wrong end of a lawsuit if these incidents continue. Oh, and if they try to remove paid items (or the corresponding receipts) from your possession? I'd suggest reporting these incidents - the Ottawa non-emergency police number is 236-1222 and, even if you intend to handle this as a matter of civil (instead of criminal) law, there is evidence that you need - such as the recordings from all the cameras Future Shop targets against its clientele - which won't be handed over voluntarily to you but may be available to police if the matter is taken with the level of severity that these repeated incidents deserve.