This has already been tried. I, personally, hated it so much that I just stopped using the self-checkouts whenever possible, because employee checkout was fast

This has already been tried. I, personally, hated it so much that I just stopped using the self-checkouts whenever possible, because employee checkout was faster, even with the wait for customers queued before me. The weight check always brought the checkout process to a screeching halt, requiring an employee to come along and restart it, even with the smallest baskets in the best of conditions.