I think that some of the responses here miss the point on this particular problem. The calipers (and in some cases the hoses) just won't let the brake fully release. It can start anytime. Seemingly out of the blue. It is not tied to replacing the pads. And by the time it gets to us, it had been sticking for a while, the rotor has gotten hot and warped, and the pads on that side are worn down more than the other side.

So what began as a dragging brake, is now an entire front brake job. So, it is just cheaper and easier (at least for me) to pull everything off a wreck for $40 or so, that some other poor schmuck just paid retail for. And since it was all just apart recently, it all comes back apart rather easily. In fact, with my battery impact and Saws-All, I can probably have the parts off the wreck in less time than it would take to properly rebuild a caliper.

You can tell from the condition of the caliper, pads, and rotor of the donor vehicle whether the pulled parts were functioning correctly. Kinda like a test drive by the original retail buyer.

In fact, we get so many of our parts now from the pick-a-part yards, Amazon, Ebay, and Rockauto, that a regional rep for O'Reilly's wanted to know why we were down to less than a couple of hundred dollars a month with them.