It happens...
Just a couple of the stories I have personally experienced...
I did a quote at one of the most prestigious accommodation spots in Melbourne on top of Mt Dandenong overlooking Melbourne city, I was referred to this guy from another client and knew they would have 10 grands worth of work at least so the initial quote was for a days work cut and leave $400. Normally i would charge $2-$3k to do the amount of work if quoting but i knew this guy was just starting a huge amount of work, things were tight and i wanted his business, so $400 was a joke but not a bad days pay 10 or so years ago...
A couple of months later after never hearing back from him I heard through best mate who's gf worked there that he had attempted one of the trees himself and cut through his calf muscle, spent two weeks in hospital and would never walk without a limp again. This bloke had done all the work on this place, amazing rock walls and was built like hulk hogan, i could picture his massive calf muscle popping open with the saw all for $400. The tree he was doin i coulda dropped in 10mins and feel like overcharging him at $100...
More recently a friend of a friend was chewing my ear off about tree work, joking about doing it all himself and blabbing on about over paid tree guys, bragging to a chic we know how he was gonna do all her trees... I find out a month later he pulled a stump out with his 4wd and it popped and came through the windscreen, he has had me over since to discuss and quote on some removal and remediation and several stumps to be ground out, head hung all low like...
It happens more often than you'd think...