Autozone, Carquest (which is now Advance) do the same thing, Oreileys loans tools i believe but dont do the check engine scan anymore that im aware of. Point is, they are all doing it. I know allot of you wont like me for this but we allow people to bring their own parts, to a point, as i would rather get something out of it rather than nothing out of it and as Joe pointed out, the labor is where the money is made.
In your case Joe, we tell the customer up front there is a 1/2 hour front end inspection charge if during the course of an alignment we find loose or worn out parts and they decline the repairs here. Then when they come back we get the alignment charge as well. This way we arent doing free front end checks for the do it themselfers. (kinda of the topic but wasnt sure if you did this or not).