In my experience(I'm with a printer), most designers I deal with are hired to design a project. They are paid to create a design and once complete, that design is the customers. The designers usually handle print/press checks for the first print as they know the project and desired outcome the best. Most designers add a mark up to the print quote to cover their print management time.
But in most cases ,after that first print, the customer owns those files and isn't charged extra for the files they paid the designer to create.
This can of course depend on your agreement with said customer. For example, if they didn't pay for design because it was a regular print run they do, but you collect commission on each time they print.
Also, it often ends awkwardly if there is surprise charges for file delivery. Make it easy for them to continue to work with you.