I once worked until 8am to get a demo ready for a client of the client. I knew the client was a bit thick, so I made some comprehensive video demos and sent them over to him, to save him trying to demo it himself. I wake up at 11am with him screaming down the phone at me:

“It doesn’t work, none of it works!”

“What do you mean?”

“I go to login and I can’t enter anything.”

“I haven’t sent you anything to log into...wait, are you trying to log into a video? Tell me you’re not trying to log into a video of a login page.”

“Uh...oh hang on, it just worked. Ok no pr-“

“No wait, what do you mean it worked?”

“I logged in fine.”

“It’s a video. You can’t log into a video.”

“Uh...alright, bye mate, thanks!”

The moral of the story is: never assume any level of intelligence on the part of a client, even if they exhibit signs of it at first. If they are paying you they will forget how to tie their own shoelaces.