We just spent a week in Amsterdam and Rick Steves' book on Amsterdam was invaluable. There are two restaurants I would encourage him to consider: Hap-hmm, which is a small famiy run restaurant that has won numerous awards, justifiably. It was extremely reasonable. It serves traditional Dutch food, comfort food. My friends thought it was the best meal we had in Amsterdam.
We went to the Seafood Bar, which Rick recommends. It was amazing. Equally amazing was another seafood restaurant, A Good Companion, where I had the most amazing sea bream ever. It was a whole fish and delectable. It cost 27 euros. It is in the Jordaan neighborhood.