Hmmmm. Much as I appreciate your desire to "fix" things, you're in a slightly tricky position as an owner of a shop. Many of these riders may just be "going with the flow" - people can do the dumbest things in groups - and alienating them by taking a hardcore stance against the group in particular may just be losing you customers. You're under no obligation to fix the situation, even though people associate you with these "racer friends", no more than a car shop has an obligation to regulate driving habits in your town.

But also as a bike shop owner you have a bit more clout than the average cyclist. You can take a stand on your own views on road riding by, I dunno, prominently displaying stickers, posters, books, T-shirts etc., your own friendly leaflets encouraging all riders to follow basic rules? whatever. I think the most constructive solution is a live-and-let-live approach - let them do their own thing (and take the consequences) while you promote your own views as calmly and clearly as possible. You are in a way representing "all cyclists", while they are just a random group, no matter how drivers like to lump them together.

If you really want to try to change their riding habits, you'll have to ensure you get in touch with someone who a) actually has a leader role and b) is open to dialogue. If you can find that person, you could lay it out saying "see, we have this problem because we're being associated with your riding habits, which we don't really approve of." They have enough "enemies" who just don't like them, they need to see how their actions are detrimental to their "friends", if you get my drift.