Generally speaking, it depends on (A) the quality of service as well as convenience factor, (B) the inventory, and (C) the knowledge base of the individuals working at the store. I'm willing to pay roughly 5% more for each one (so a maximum of 15% probably).
No LHBS has ever been rude to me. But there are many that operate odd hours, at least for me. One near me opens at 11 am and closes at 6 pm. It's sometimes difficult for me to get there. Another one only offers "pick up" (i.e. no browsing) from 4-6 pm, and browsing on Fridays and Saturdays. To me, if I have to figure out a week in advance how I'm going to get my schedule to line up to make it to the LHBS, I just buy online.
For knowledge base, there are so many times I've gone into the LHBS where they had no idea what I was talking about. They employed a local college kid that brewed 5 batches to ring things up. When I ask for an erlenmeyer flask, or ask for a good substitute for Maris Otter and they give me a blank look, I just move on. I brought a 1970's mead recipe into one shop and asked for help on some of the ingredients they asked for (Urea and a few other things that aren't used anymore) because I thought it'd be neat to brew a 50 year old recipe, and they had no idea what literally any of the ingredients were except for the honey. They told me not to brew it. I walked out the door.
For inventory, it's a must for me. I went to one LHBS with a recipe, and they had to "substitute" 80% of the ingredients for things they had in stock (C60, Golden Promise, a hop that I can't remember right now), which means I brewed an entirely different beer.
But oddly enough the larger the inventory, the cheaper the prices. I prefer to drive 1 hr away to a big homebrew supply store, driving by 4 smaller ones. Their prices are cheaper than many online retailers, and they have literally EVERYTHING I could need. Amazing inventory, fantastic prices, amazing customer service, and a top notch knowledge base of employees (some of which work in the brewery next door). Tough to say no, but can't always find the time to make the drive.