In Indiana by law we are required to warranty our job, material included, we cover this by material markups, to not have this option you could be setting yourselves up when something goes bad down the road, as your state might also have a law like this.
I did one time allow a friend to supply the material on an apartment job, about 5 months after the job was done, they had a light that would not work right, so she called me and told me I need to take care of it because it is under warranty, I told her I didn't supply it, Oh she said she will get what I need but labor should be under warranty, I said oh really, well then her attorney called me and stated to me I was committed under the law to warranty the job no matter who supplied the material, checked with my lawyer and he agreed it wasn't right but it was in the law, so I did replace a bad switch but it was the last time I ever allowed the contractor/homeowner supply the materials.
Case law now says we have to warranty our work and only the material we supply, so now I have a disclaimer in my contracts, that says I don't warranty any material I don't supply, and labor is not included.
But I have still changed out a few ceiling fans just to make the costumer smile.:grin: