Angor decided upon the three conditions after going over careful considerations. The test-fly was not dangerous to Toby, so this was an easy favor. Angor never intended to go overboard.
Still, asking too little would leave Dave an impression that "asking Toby for help is too easy" which in turn encouraged Dave to return with some other strange products to test on Toby again. That was why Angor needed at least one condition which tested Dave's limits, to warn him not to go overboard with his requests.
With these three conditions, Angor both told Dave when to give up AND earned some profit out of them.
Since Dave already agreed, Angor willingly opened the garden door and invited Dave inside.
