You know what, I put that poorly. You're absolutely right, laziness is perfectly valid. There's nevertheless a psychological difference between (variations on)

You know what, I put that poorly. You're absolutely right, laziness is perfectly valid. There's nevertheless a psychological difference between (variations on) "sorry dude, too many things on my plate this week" and "No.". There's nothing about the former anyone one can argue with, but it shows that you value basic human mutual understanding. If the couch-owner truly lacks self-awareness, to the point where they constantly badger you with unreasonable requests (we all know that one guy), then a "No." isn't going to enlighten them either – in that case, you do them a favour by respectfully but explicitly informing them that their request is unreasonable.