I tip my LBS when I ask them to do stuff out side the norm. I've looked at purchasing several used bikes. I generally have the seller meet met at the shop, I ask the wrench to look it over and tell me his thought and what it would cost to make the adjustments that I need. new tires, cassette, etc. Some times a $1000 road-bike may need $20 or $300 of adjustments to get correct fit and feel right. To me this earns my wrench 20 bucks whether I buy the bike or not. So far he's made 4-50 bucks off me and knows exactly what I need in a bike. I bought the bike that needs fewest adjustment and fits the best.