I think your venom is misguided because I actually agree with you. I have never understood the folks who make special trips to the US strictly for shopping. I can't see how there are any real savings to be had after you've figured in the exchange rate, cost of accommodations, cost of transportation, time, etc. Furthermore, considering that one can claim $800 duty free to start (after 48 hrs absence) and then a special duty rate after that, I just can't see how it's worth it to lie to a Customs officer and risk huge fines and duties or forfeiture.
Nevertheless, I'm not sure it's up to a private business in the US to take it upon themselves to report someone, without any evidence they will commit a crime, to the Canadian Border Services Agency. Just because a Canadian spent a lot of money in a US shop, does not mean they aren't going to declare it properly. What if the person who had patronized that shop was preparing to declare everything and had all the receipts ready, but had his vehicle ripped apart in secondary inspection based on a helpful tip from a US business? I certainly wouldn't go back to that business, nor would I recommend it to my friends based on the fact that:
1) they caused me undue hassle at the border for no good reason; and
2) they obviously have no respect for me (the customer) in automatically assuming I am a criminal.