It's bad business, either way. Not only for his own shop, but for the entire franchise.

Plus, it puts Christians in a bad light. Makes them look small-minded and annoying.

What the business owner should have done is "turn the other cheek" and give the guy his $15 discount anyway.
Kinda makes you wonder why he didn't do that . . . unless he actually wanted to cause a controversy for some free publicity? Who knows?

But if this is how Christians behave, then I'd just as soon take my business elsewhere.