I recently stamped my new daughter's room with the DD Butterflies. It turned out beautifully. I know everyone says to use acrylic paint, but I actually used latex paint samples from Menards. I used paper plates to hold pieces of 2 ply felt and applied my paint to those to act as a stamp pad. I was stamping with four colors (light and dark pink and light and dark purple), and I was stamping on four walls, so I just left the stamps in the paint (stamp side down) so that the paint didn't dry on the rubber. I didn't have any trouble at all cleaning the paint off the stamps since the paint never dried. I was able to stamp all my butterflies in a little over an hour. If I stamped an image and didn't like it, I had a damp cloth at the ready to wipe the paint off the wall. It came right off and didn't damage my base paint. I was very intimidated in the beginning, but after applying the first few butterflies, I got more and more sure of what I was doing. I say tell your customer--just go for it!!
Here's a picture of my daughter's wall
Gallery at Splitcoaststampers
Hope this helps a bit!