What happens when a pax is made to check their carry-on and:
1. They have already checked one bag. Are they then charged for 2 bags?
2. Their >7kg carry-on combined with their checked bag then exceeds their total checked weight allowance. Are they then charged for 2 bags?
I have some related experience here. The answer to your first questions is yes. The answer to your second question is VA charge per bag which can be up to 23kg (more for WP).
I was prevented by security at CBR to travel with fishing reels (spooled) in my carry on, despite having done so on many many previous occasions. They're valuable, integral to the purpose of the trip, and with a couple of other things in the bag the total weight would be around 15kg.
I had to check the bag and I'd already checked two 23kg bags - ie as a VA gold I was at my "limit". The checkin staff informed me of that but took some pity, presumably, and checked it for free "because I'm a gold", thus saving me $70.
So there is some financial incentive for airlines to go down that path. And some incentive to stop hiring staff with philanthropic tendencies too.
As an off-topic closure to my story, while checking the offending bag/reels, the security woman and her "boss" both came up to me at the VA counter to share the evidence on a phone that they were indeed correct - buried deep in the CASA web pages is a list of banned items that included fishing line. Then a guy on my flight brought on a cricket bat as carry on.
Back on topic - It is this ridiculous inconsistency by airline and airport staff, some of which is rooted in folly, no logic or obvious contradiction, that causes angst among travellers and can lead to aggression.