If you've had the same amount of customers come in or more than years past, yet your profits are falling, you really have no choice but to raise your rates (I'm not sure if this is the case).

But I guess what you mean is, only raise your prices on people that bring their own stuff in. I think it's fair, but only if it's $5 to $10.

This might seem stupid, but If the product I brought in I only saved $10 on it and you charge me $10 more to install it, then hell I should have got it from you in the first place.

But not raising the labor on your loyal customers, I don't think that's fair. If they are your loyal customers and they come in every month to install something, maybe they have more money to spend on mod than others? Perhaps their cars need more maintenance? Maybe they are out of warranty and that is why you see them more often?

I think it would be better if you charge the same labor rate for everyone, but give a discount on parts to those that visit you once a month or something. You know, kind of like frequent flier miles. Every 5th oil change is %10 off. Something like that.