You may want to explain that in order to have a no or low maintenance tank requires the tank to be extremely balanced in respect to stocking, water chemistry, and ecological soundness and this all adds up to a lot of money on the front end and usually ends up with a rather boring looking tank( unless it is a rather large tank.) In the long run, it is better for the fish,(
IMO) to do some routine maintenance than none at all.
Again,
IMO, it's better he not set up a tank at all than set up one that will only be a poor environment for the fish to live in.
The reality is that not everyone is a good fit to own a fish tank. Better they know up front than in the end.
Hope this helps