Are free headlight restoration demo’s a good way to advertise to used car dealerships?
Sure. However a more efficient approach, would be to have a demo light to carry with you. Approach the manager with a light half restored. You won’t be denied the chance to show him your work because you will have it right there with you.
It will also save you much time from doing no pay demo’s.
To prepare a demo light find a corroded one from a salvage yard or one from a body shop that has been damage on the back side (one they will throw away). Mask off half of the light and restore just one side. Use a canvas bag to carry around so the restored side doesn’t get scratched up while in transit.