Recently we have had some incidents where after our customers have received product, to come back (sometimes months) later on and demand we modify the product to new dimensions, add services, etc....  This is always with the threat of no future business of course.

The system that we use is after receiving the PO, we send an approval drawing showing sizes, features, colors, casters, etc....  The customer then sends us an approval email and we begin production.

I was wondering what other systems people use to combat this from happening. We are considering requiring the customer to sign and date the approval drawing, and then email - fax the drawing back to us ???. We don't want to offend any customers as most are loyal good people, but feel that we are not financially protecting ourselves. We are discussing whether to add legal language onto the approval drawings; or do we add it to the original quote?

Looking for ideas here.