About once per month. I purposely set expectations low by saying it may take a little sanding. That lets me over-deliver since it's usually a perfect fit. Also, ShapeWays has a decent refund policy and customer service for stuff under their responsibility.

Also, anything that comes up that takes significant back and forth with a customer, I immediately add to the iFixit writeup. All the troubleshooting steps at the bottom were a result of questions that came in at the beginning. This was a lot of work up front, but it's thankfully just a trickle now.