I am a bike tech and we really appreciate a little extra. We don't get paid a lot. I try to go above and beyond what customers are paying for every time I touch a bike, and it's good to know how much they appreciate it. If I have enough time, I sometimes I put a bike up in the stand if I have time and do a quick adjustment on the bike, have a friendly talk with the owner about the trails he's been riding, talk about upgrades he might be interested, or injuries we have suffered. sometimes I get advice about trails I have not yet ridden. if the adjustment takes less than five minutes, I usually don't charge the customer in hopes that they will continue to come back and support the shop. and if I am lucky, they slip me a $5 bill. I have received alcohol as a tip before at other shops but I know my current management really frowns upon that, so be discrete!