Economics 101: Every dollar you spend is a vote for a seller and their products or services. Vote against undesirable retailers by not spending money with them.
Sounds like the guy is either greedy or desperate with a rule like that.
I've also seen an LDS owner who will teach the class, but is continually critical of gear bought elsewhere. Leaky mask? Snorkel pulling your hair? Got a cramp from kicking fins in cold water? The response was always the same: it's the "other" brand from the "other" store that's causing the problem. That's not as bad as refusing to teach a class with gear purchased elsewhere, but still unprofessional...
Sounds like the guy is either greedy or desperate with a rule like that.
I've also seen an LDS owner who will teach the class, but is continually critical of gear bought elsewhere. Leaky mask? Snorkel pulling your hair? Got a cramp from kicking fins in cold water? The response was always the same: it's the "other" brand from the "other" store that's causing the problem. That's not as bad as refusing to teach a class with gear purchased elsewhere, but still unprofessional...