Are they doing something for a reduced or free rate for me, or in some way going well out of their way to service me? Are you staying late to squeeze my work in? Moving me to the front of the service line? Are you going well above and beyond to address me specifically? In that case, I would consider it if the situation called for it.

In general? No. Its a business transaction, you do the work, I pay you, like any of the other numerous business transactions I do on a daily basis. I've personally never understood this necessity of friendship that people will put into their local hobby shops. I stop at my local McDonalds every morning for a breakfast sandwich on my way to work, I know the folks at the counter as well as I know my LBS employees, and I don't think a single person here would think it normal for me to drop off a six pack for them as thanks for their work.