well...i read my school's application or whatever to become a preceptor, and apparently they are paid/reimbursed/whatevs $300 per student per rotation. In fact, on my first rotation at walmart, my preceptor told me he went out to buy some expensive shirts as soon as he had gotten his check that month...
My guess is it depends on the school policy and the individual preceptors (some may waive the fee and be willing to volunteer their time...). Generally preceptors are paid a small fee. If a rotation is any good, it takes A LOT of time to teach a student (as a colleague of mine who is precepting for the first time this year is learning!) and benefit from them working, or trying to, is generally negligible if it is a four- or even six-week rotation. Rotation students are definitely not free labor, though they certainly like to think of themselves that way (I did too, when I was a student on rotations, and grumbled about having to pay tuition when all I was doing was working, as I thought).
Of course, there are exceptions, and I heard horror stories about students being used as free labor and told to man the registers, etc. when they were at the retail location, but if you find yourself in such a situation, that's when you call your rotations coordinator and ask to be transferred to a decent place ASAP. Even if you got stuck with a retail rotation (I heard some schools have them mandatory) and you have been working retail for years, there are still things your preceptor could teach you, which you don't see, or have you do more clinically-oriented projects. And in other settings it's even harder to turn students into productive free labor than in retail.
And yes, the preceptors were listed as adjunct clinical faculty for school's purposes at the three schools I know firsthand.