Hi S.,
Sadly, some people cannot comprehend simple instruction these days, or much more beyond simple breathing.
Don't worry though, soon everyone will have battery operated mowers that will simply activate when the grass gets 3 inches tall. Camera sensors will control it, and people can always expect a perfectly manicured lawn. LOL
A phrase that I used (quite often) years ago as a military instructor was, they "could break an anvil with a feather".
I agree with you, that is why nothing leaves my shop repaired or sold as used unless they operate it first, if they just cannot understand safe operation, I will not sell to them after I see them fumbling too much.
Another pitfall I avoid is when a "representative" or family member tries to buy a used machine that they will not be operating.
Here lately I have been entertaining the thought of only specializing in portable generators, ATVs and UTVs. They seem to be the most profitable in my area. Besides, most riders and push mowers I see are damaged beyond economic repair, so I quit trying to "save them all".