I can't imagine any bike mechanic worth his or her salt not wanting to fix something properly, and being happy for the chance. It should be a matter of pride. Maybe it helps if you know that bike wrenching, especially derailleur adjustment is often not a "there, that's fixed once and for all"-kind of thing. You need to tweak a little, and try it, tweak a bit more, and try it again. Telling them that it still rubs is not telling them that they're lazy or terrible mechanics or did something wrong. You're just telling them that they were a little conservative in the adjusting or the cable stretched a bit more, and they need to finetune it a bit more. It's not really a complaint, so just smile and tell them you need 10 more minutes of their time, please.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett