I get this attitude all the time. My reputation as a "computer guy" spread through the neighborhood like wildfire. Next thing ya know, people are knocking on my door at least 3 or 4 nights of the week expecting free tech help.
My best response is to demand an annoying chore in return. For example,
Neighbor: "My DSL isn't working...you got a sec to check it out?"
Me: "Sure! I'll get started after you have finished cleaning my gutters! You've got a ladder, right?"
They usually smile and think you're kidding at first. If you don't budge, you've either got a paying customer (via services) or one less knock on your door when you're trying to eat.