+1 jonba
I quote for a finished job, you cant quote for something then change your mind because its not going your way, if the decorator was in any doubt he should have quoted for the third coat then maybe reduced the price if it wasnt needed. You cant lose a job via price if you always quote the lowest price it would take.
But if you dont talk to him about it he wont know and then cant correct it to your standard. give him a chance to put it right 1st.
Edit: he really should have quoted for 3 coats on top of that primer though, very rarely will 2 coats cover on that.