Yeah, I'm not trying to call any specific user out on this, it's just that:
a) Most visitors or new residents to Japan don't initially know the sizable discrepancy between many western cultures, especially American where "the customer is always right" and the Japanese "the customer is God...as long as he plays by the rules".
I read a story elsewhere about a guy who got blackballed by an AM girl because he engaged in fairly vigorous throat-fucking with her. She didn't complain, but after that session refused to see him again. He was lucky that AM still answered his phone calls.
b) Despite the fact that some sex play is more or less legal and red light districts are ubiquitous in larger cities, most of them still do business in a grey area of the law. Unlike US law, which more or less intends to maximize justice, Japanese law more or less intends to maximize harmony. There's lots of P4P practices that, legal or not, are allowed to continue as long as they don't disrupt society too much. You don't just see this in the P4P area either- just look at immigration, taxes, etc. Therefore there's a difference between the 'law' and the unwritten but more important 'rules'.
Japanese men that go to the sex shops know the rules. Most foreigners don't know the rules. And if you are from a 'customers first' culture, a customer not knowing the rules and having a sense of entitlement is a really dangerous combination from the perspective of a sex shop owner. Those customers that think they are getting scammed or ripped off (by not getting the FS they read about on some review site, etc), will do things like make a ton of noise at the front of the shop, threaten to go to the police, etc. This only brings trouble to the shop, because it's bringing attention to the shop (disturbing the harmony of the area).
I think that this, more than almost any other reason (except for maybe the racist viewpoints of other customers) is the reason many shops won't service foreigners. Notice that the number of places that service foreigners who speak Japanese is MUCH larger than places that won't. The people that know Japanese probably know 'the rules', and if not they can be explained, or they can read them upon entry to the shop.
This is not to say you can't register your disapproval in ways that are socially acceptable in Japan. Generally, this means not going back to the shop again, not seeing the same girl again, writing a bad review, or if you want to express disapproval directly, learn some Japanese and do it subtlety and with some class.
