I bought a few items at Bass Pro Shop a few days ago. The nice lady put everything in a bag, then wrapped their logoed tape around the handle so that the bag was closed. She also put a sticker on the soft drink I purchased. Lowes, Home Depot, and a myriad of other retailers do similar. The local grocery store puts stickers on anything not bagged. And all of this occurs within a few feet of the exit. It's called "loss prevention."
Now you are carrying an expensive piece of merchandise from some booth hidden within the bowels of a gun show, well outside of where anyone monitoring the door can witness your purchase, and you are bent out because she wanted to see proof you bought it? She may have exercised poor tact, but she didn't call you a thief. But, if you could not produce a dot she probably would have requested to see a receipt you had crammed down into a pocket. It is easier for you to show a dot on the item. It keeps the exit clear if she doesn't have to stop everyone to check receipts. So the dot policy is better for everyone. Of course, if you couldn't produce a receipt you would probably get to meet the security detail...
Then again, whining generally is the path of least (personal) resistance.