We don't have "scraps." We keep a small box of cut-offs that are large enough to warrant not throwing away.
I will sell vinyl off the roll, but I charge a min of $20.
I'll also resell entire rolls for 2x my cost.
We do this exact same thing. We will sell vinyl, substrate, VHB tape...you want it...we got it. But we do so at a retail cost to the customer of a 100% markup over wholesale. We sell 24" calendered vinyl at $6.00 a yard, economy cast at $9.00 a yard, and premium cast at $12.00 a yard. We stock quite a few 4' x 8" panels as well because we always take advantage of sales and stock items ahead. So if we get 1/8" ACM panels at $42.00 a pop and can resell them for upwards of $140.00 a panel, with no work involved, I'd be happy to do it.
Now back when I was a tattoo artist, it was way different because it's generally considered unethical to sell tattoo supplies to the general public. Some shops will argue that they are only getting safe, sterile equipment into the hands of those who are going to tattoo themselves and others anyway, but I've never considered that practice ethical.
I don't really consider it an ethical matter selling sign making supplies to the general public so I would do it all day, every day if I could. Most times, people who ask if they can buy materials aren't using them for sign making, scrap booking or anything that has to do with plotter cutting. We sold 4 yards of calendered black vinyl last year to a guy who used it across the back of his aquarium, which worked out great for him. We've had people buy it to make paint stencils, wrap a bruised up helmet visor, and we've sold coroplast panels for something that had to do with dividing a cage for hamsters? Hahaha!
As far as the off-cuts, we also save our larger pieces rolled up and sealed in a plastic tub. The tub is getting full. I would LOVE it if someone would come buy it up at roughly $6.00 a yard. We seldom ever wind up using much of it, anyway.