I can't offer any info on that particular teacher, but you might want to take a look at the tutor listings on gmatix.com if you want more options--there were plenty of other New Yorkers listed there last time I checked. Not sure how many of them are in your price range, but it's probably worth a try.

It's definitely a good idea to hire a GMAT specialist instead of a general math test-prep guy, but it can be really tricky to tell them apart. Try asking the tutor to explain the difference between the GRE and the GMAT--he should be able to give you a very long answer. Or maybe try to see how well the tutor understands the composition of the questions on the GMAT--a general math guy will probably overemphasize geometry formulas and (maybe) combinatorics, but might under-emphasize number properties.

I hope this helps, good luck with your search!