Being published did not help my sales. I was published in a book of tutorials. The target market would be other jewelrymakers and I rarely sell my work to others in the same field. I did get a few emails related to the publication, but those were from people looking for specific materials.
I was paid after receipt of my item by the company. Seems standard. From their perspective, they could pay you for the item and then you could flake and not send your work. I've only sent work in once it is accepted for publication, but never to be considered for publication.
Also, make sure you have a contract.