I would be surprised to see a bluff but I never fold there either.
I just put my opponent on a hand I can beat and click call.
"The guy has ks4s and we beat that."
I would be able to make so many more disciplined folds if I could see…
What reg opens 53s from the CO?
How does a reg get to the river with 44?
75s is a fairly loose CO open and will almost always cbet the flop.
22 is the only hand that makes sense to me.
What did he have?