Or perhaps his company doesn't want the hassle of workman's comp or health insurer dealing with a possible injury obtained outside the scope of his 'normal duties'.
I try not to obsess over potential liability issues, but the threat of litigation is constantly hammered home these days. For example -
We had only about three inches of snow here in Northern Virginia, and much of it had melted from the pavement by this afternoon.
That didn't stop some panhandler from knocking on my door to ask if I'd like him to shovel my smow.
When I refused, he commented "If someone slips on your sidewalk, they can sue you!".
I replied "Thanks for the advice, and kiss my ****!".

Happy Motoring, Mark

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DrDKW