I'm curious..."amazed at his behavior" ...why? How? What is so amazing about a big, driven work dog that needs a job? Of course, you should be aware that such evaluations are very serious affairs and that many people who believe that their "Fluffy" is the next Rin Tin Tin or such get their feelings hurt when the big lug is taken to a strange place with a few distractions, etc. and someone new to him throws that ball, and they see him sit there as if to say "OK dude...you threw it, now you get it back!"
If he passes first muster...most don't...they will likely take him home for a while and work with him a bit more, then they will have to spend somewhere around $500 or so for xrays, shots and a full CBC just to know exactly what they have to work with health-wise. Many more will fail here as well. The training put into a good sniffer dog over the years will run into the thousands of dollars if you consider all the man hours involved. That is why they want 'em young and healthy...longer service life.
Most trainers will prefer that an active-alert dog have very little obedience...almost none at all, and other detector-only dogs only a little more, so no problem-o if his OB is poor or nonexistant. What they really...really...wanna see is a dog so crazy for the ball or toy that if the world was ending around him and you threw that ball, he would be unable to resist going after it one last time! (and no, I an not kidding about that!)
I just placed a young male Lab (9 mo.) that would nip you if you teased him with the ball and did not throw it quickly enough to suit him. He would hunt for 10 minutes easy in briars, high grass, etc, for a ball...and he is still a very young pup. Excellent prospect, and he was given away by some folks in similar circumstances to you. He will be a LEO before too much longer I think! (No, I did not make one cent from the transaction although I know several brokers who would happily have paid me $500-750 for him if I had wanted to take the time and trouble)
Good Luck to you and your boy!