Richard101 - for the record most brokers CAN tell the difference between the aircraft types, if they can't then they shouldn't be doing the job! I think you've missed the point a little. Brokers are not the ones questioning the age of the aircraft, it's the clients they're acting on behalf of. If the client wants a new aircraft, then that's what you have to offer.
The interior of the aircraft isn't such a big deal. Sure, you'll want to avoid anything that's too shabby, but I certainly wouldn't say you can judge how good an aircraft is by how new the seats look, that's not logical, it's like polishing a turd - might look nicer, but it's still a turd underneath!