I bought a used headboard for $10. It was poorly designed and the pieces didn't fit well together, which is pretty bad since its original price is around $150.
The headboard has a small shelf with a ¾-inch back panel, but the pre-drilled holes don't line up on the left and right posts. As a result, the panel forces the whole headboard askew.
I took out the panel and designed a small post to replace it and prevent the top piece from sagging. The foot of the post had to be angled slightly to account for the shelf sloping toward the back, and there are holes at the top and on the back for the original furniture cams and screws, which I reused to connect it to the top piece. There's no need to attach the post at the bottom, since gravity keeps them in place.
It took a few tries to get the sizing right, but I'm very pleased with the end result.
The author marked this model as their own original creation.