In my experience, people at a good LBS will treat you well no matter who you are, because they want to encourage you to come back again and again.

If they really don't respect you, they're not worth the effort. My favorite bike shops are not the ones closest to my home, they're the ones that treat people well.

But if you're just concerned that they won't respect you, even though you have no evidence of a problem, then take a deep breath, hold your head high and go in and talk to them. Customer service is their job. If they suck at it, that's their shortcoming, not yours. Try to visit when they're not busy -- the folks at my LBS are quite chatty when they're not in the weeds, and that's how they get to know their customers. And frankly, I'm pretty sure they understand and appreciate that they make more money off of me because of all the things I don't know about bikes, because I need to pay them to do things that some cyclists will do for themselves.

As for your drive train problem, you paid for a service so you have every right to bring the bike back and ask them to look at it again. Since you can give specific examples of the problem, it will show them that you know enough to be taken seriously. As long as you're friendly in dealing with them, they should treat you well.

And if they don't, it's their loss.