I usually just let people like this go but this one was just too stupid so I sent him this message via gumtree:
"Hi Paul,
I'm just checking; that "Custom slasher" you are selling is a joke right?
If not it's INCREDIBLY dangerous and I really hope you scrap the base.
I am a fellow lawn mower refurbisher and reseller however I am very concerned with the safety of the machines I sell. Removing the front section of the mower can easily send projectiles towards someone at an incredible speed. The exposed blades are again an extremely dangerous issue. The lip on a mower is designed to stop a blade should the bolt sheer. Imagine a blade flying out of the front of that "machine" at 100 miles an hour towards a child.
Unfortunately people like us have a very bad reputation because far too many people take short cuts like this "Slasher" and miss match parts to make a quick dollar. Obviously whatever you do is your business but please think of the safety of others. Most people don't think of the safety of a machine they buy 2nd hand but whether you are a business or a private seller you can be held legally liable for damages caused by a machine you sold. This can also include criminal charges.
Again I ask you to please remove the slasher from sale even if it is a joke as you may give someone unsafe ideas.
Pete"
He responded with: (I censored his language).
F#@k off idiot.. make Australia great again..
Then clarified:
"&&& just to explain. Only a fool opperates dangerous machines around children .. is sumthing majoraty must know.."
Guess he doesn't have public liability insurance. Also since he is so sure it's safe he must be an engineer so I guess I'm worried about nothing

At least at $200 it'll never sell anyway.
Pete