Find out the internet price for the accessory and then work with your lbs if you want to buy something from them in town. Lots of times my lbs worked with me on the price. Smaller gross profit margin than normal is better than none at all for them.

I think it's good to balance both internet purchases vs. lbs. There are good deals to be had with either if you look hard enough and do your research.

Plus, sometimes you need an lbs in your corner if you ever have a warranty issue or need something fixed on your bike ASAP. Familiar customers always get more attention and preferred treatment. That is, unless your a dick.