In my experience, pollenless sunflowers still produce seed. I've read that seed will grow, however chances are it will not be another pollenless sunflower.

If you're not planning to grow row upon row, you could deadhead, or cut off the flower heads after they fade but before they produce the seeds. But if you're planting a lot of them I suppose this wouldn't be an option. If it is an option then I suppose it would be better to go with a 5' variety rather than an 8' variety so they'd be easy to reach.

If you are growing them to sell, you probably are planting new ones every week to 10 days. When you cut them, you might make two passes in a particular group, as they won't all be ready the same day...on the second pass, cut everything that is left, and there won't be any to go to seed.

Promise your neighbor you will cut all the heads before they set seed. Do that and you've got cutflowers plus a happy neighbor.