Once the client is displeased, it is very difficult to remedy the situation. In an attempt to correct a perceived defect in manufacturing, installers resort to dusting roll ends with chalk or tempera, coloring with markers, or spraying with acrylic paint. Many installers claim this provides a solution. From a business standpoint, this is an unsound and possibly costly practice. By adulterating the material, the installer becomes liable for any damage or unsatisfactory result.
Some manufacturers are less than cooperative when problems arise to begin with.
Treating wallcoverings with caulk, ink, or paint will give them all the reason they need to leave you out in the cold. If you or your client are overly concerned about seams, perhaps paint would be a better decorating solution than wallcovering. If your client doesn't have a problem with the seams on their own, creating one doesn't serve either of you any purpose. Repairs during installation are far easier than those performed after the adhesive has dried. This can be especially true when less than adequate wall preparation has occurred.