Guys, I have to say if you showed up in my shop in one of those shirts I would not hire you.
Aircraft mechanics are the only federally certificated trade. We are PROFESSIONALS. If you want respect (and the money that goes with it) you dress the part.
If you want to dress like a low-paid garage monkey with a dirty rag hanging from your pocket, don't complain when you're treated like one.
Dress the part, learn everything you can, and don't work cheap. Don't give away your time on weekends. You're killing the profession that way. Charge real money for real services, you'd be surprised how well customers treat you once they view you at their level.
Most airplane owners are better off than the average guy, and expect to pay well for quality maintenance. Quality maintenance does NOT come dressed in a t-shirt. Polo shirts or other appropriate work wear are important for your image. The better you appear (and perform), the more you can charge.