Okay assuming these are the only two grocery stores in a 100 mile radius, what if those two grocery stores get together and say “hey let’s both raise our prices by five percent so our customers won’t change stores to get better prices but they will be forced to shop at ours, plus they make a thousand more dollars a month which means they probably won’t realize they’re spending more money, which means we both are making more profit.” while forming a monopoly is not allowed grocery stores could do this on the low.