Contractor says I can't buy my own materials

[Gregory Calloway]

Good morning,

I have a pretty reputable contractor that I have a bid with on a project and I asked him if I can buy my own materials which would save me on the mark-up. He informed me that he can't because he's not supposed to for insurance purposes. If there are any workmanship or issues his insurance wouldn't back him on coverage. I've never heard of this, can anyone corroborate this?

Thanks!