I agree with having the shop take care of it but since you brought it up....
It would be difficult to prove who was at fault. I don't own a steerer cutter, since I usually use a pipe cutter on threadless tubes and seldom have to work on threaded steerers anymore, until now. So I gave them the measurement on the plus side and they made the cut. If anything I was planning on adding a spacer. I like to do as much of the work as possible so only wanted them to make the cut as opposed to giving them the bike. I would have taken it apart anyway when I got the bike home to make sure they greased, assembled and adjusted it correctly.
Small town, small shop, I want to keep the peace since I am always open to the possibility that I didn't communicate things to them clearly. Definitely not the preferred way of doing things and I have convinced myself to purchase some headset tools which are about the only items I now need to complete my collection of bike tools.
So now that you know the entire story....