If you look at the marketing and identity guidelines for the Product Bezels, it says:
"Use Apple product images “as is” and without modification. Modifications include adding reflections, shadows, highlights, or graphic elements that appear to enter or come out of the product screen; cropping, tilting, or obstructing any part of the images; animating, flipping, or spinning the images; or creating buttons or icons with a product image. You can place promotional copy or violators beside the product images, not on top of them."
And then in their Terms of Use:
"Except as expressly provided in these Terms of Use, no part of the Site and no Content may be copied, reproduced, republished, uploaded, posted, publicly displayed, encoded, translated, transmitted or distributed in any way (including "mirroring") to any other computer, server, Web site or other medium for publication or distribution or for any commercial enterprise, without Apple’s express prior written consent."
So I think by selling mockups using their bezels, you'd be violating both the guidelines and terms of use.
https://developer.apple.com/app-store/marketing/guidelines/#section-products
https://www.apple.com/legal/internet-services/terms/site.html