Djpic.
You say "has he sought advice from other pilots that have flown it".
My initial post was based on C150 aircraft stalling characteristics in general, although I have flown this type and noted a significant wing drop tendency in some. In fact a CAA inspector advised that a 500 ft height loss is normal in a C150 during a full flap power on stall entry and recovery. I would be thoroughly alarmed if this observation was true.
Seeking advice from other pilots who have flown a C150 on what they think, will elicit a wide range of opinions - which is why new instructors in particular, who may have hardly 250 hours in their log books, need reasoned guidance on what constitutes an unacceptable wing drop characteristic.
Regretfully there is no shortage of clapped out Cessna 150's that would never pass a searching no-nonsense airworthiness check by a diligent inspector. Never happens of course. Yet instructors and their students accept these aircraft as the norm, and because that is all they have ever known, happily accept these aircraft if the hiring price is right and the hours are logged.
Unexpected wing drop at point of stall can usually be traced to mis-rigging. This costs time and money to rectify especially if the pilot has the temerity to log the defect officially. As Mad_jock alluded earlier, now we are talking job security!
Perhaps the acid test of such aircraft is would you be perfectly happy to send a student on their first solo, knowing the aircraft possessed a savage wing drop at the stall? A courageous decision Prime Minister...