One hole is not enough. Really, these should be vented panels. Or at least 1 sq ft of venting at each location, but 2 sq ft would be better. If it were me, I would pay this guy and send him on his way and then take care of it myself. There is time and materials in cutting these holes and putting in venting, so his extra charge is not that unreasonable if you were paying by the hour - what is unreasonable is that he did not do the job properly.