skydriller, funny you should mention that. Before the whole "pay for emergency exit seating" trend started, and you asked for an emergency exit seat at check-in, the check-in staff would size you up first and check whether you were suitable.
On certain flights I've had the situation where CA's would do a call for any other passengers who would like to switch seats for an emergency exit row (usually AF flights) because a pax in an emergency exit seat was not suitable for the required actions (or was not willing to perform the actions). Then it'd be a mad scramble for a while until everyone was settled again.
That kind of discretion by check-in staff has to return for emergency exit seating... I'm capable, and I'm happy to pay for the privilege.
S.