this concept of "substitution" that you're aggressively pushing does not exist in real life or in the real life habits of consumers, it is a marketing construction that nobody wants. further, i don't remotely understand what the fuck you're even trying to say when you use ridiculous language like "store loyalty". what the fuck does that mean? that i'm going to overpay for something because i'm "loyal"? what? i think that what you're trying to actually say is that you think i'm fucking retarded.
drop the issue. if you don't have an item in stock, take it off your website. it's false advertising, you should be held accountable for that and somebody is going to do it if you don't stop with the bullshit of selling people something specific and then trying to deliver something else to them by using the bullshit orwellian excuse of "substitution".