As an architect, I'm often asked for advice, and usually give it. Id be pretty un-neighborly not to. But it's a minefield. Even if I don't charge for that advice, I can still be sued if someone follows it and suffers loss or expense because the advice was bad. My insurer therefore doesn't like me giving free advice, even to family.
Doing freebies on the tractor is no different. If you make a mistake and someone suffers loss due to negligence, they can sue.
You have two protections: the first is to limit liability by operating as a limited liability company. Then the limit of your liability is essentially the assets of the company. If you're doing freebies, you'd likely have to demonstrate you were acting on behalf of the company and not as a private citizen. That might be tricky. If your sued as Mr Citizen, you can be stripped bare. Always best to operate as a limited liability company.
The second protection is insurance. An indemnity policy for third party damage of, say, $3 million will have a pretty hefty deductible. So make a mistake and it will still cost you even if it costs the insurance company more. And if you seriously injure someone and they are awarded damages in excess of the amount your insured against, you will be liable for the shortfall.
So the lesson is: if you do freebies (or even if you always charge), be aware of the risks, get limited and get insurance (preferably with a low deductible).
Edit: There is another course you can take. That is to get those you're doing a service for to sign a waiver. Example: some neighbors of ours use our riding ring in winter because during the wet season theirs is always waterlogged. We're not going to be un-neighborly and say no but we're not going to suffer the expense of insurance because we're doing someone a favor. So we have them sign a waiver. We prepared it ourselves but we had it vetted by a lawyer and my wife ran it by our local horse association. Both advised it would stand up in court. None of our neighbors has had a problem signing it.
