The only faux pas is thinking there are specific LBS rules. They are a commercial retail outled and you are the customer.

Other than the GENERAL stupidity things pointed out by UADave, Rev.Chuck and Louis, when you go into any commercial retail store YOU are the boss as the customer.

Haggle as you feel you need to; the bike shop isn't going to sell you anything if they don't make some money from the sale. So, if you're haggling and they agree then you're both getting something from the deal. If they don't, they're not being buttheads or anything, it's just not in their interest to do business with you; and there's nothing wrong with that whatsoever.