There's been plenty of posts on here about being people turned away when they try to enter the ground.
My guess is that most of those who are punting tickets on are not STHs but fans who are "members" only as they are opportunists. They buy a ticket only to punt it on for a profit. If they are...
Club have been refusing entry to up to 100 people at home games this year, all who have bought tickets from unapproved sellers.
The club find out the seat details and then block that ticket from entry. The ticketholder tries to scan in and they are refused.