It's time to separate issues .... and perhaps chat with an attorney. It mayalso be time to call the shopkeepers' bluff, and let the judge decide.
First, you say you were paid. I'd say this removes you from the fight. What remains is a dispute between your friend and the shopkeeper.
If your friend is required to have a license to plow snow, he may not be able to collect unless he has that license. Even without the license, he is still liable for any damages he may have caused.
The shopkeeper can sue only for damages; your local laws will define what sorts of damages he may ask for. Chances are, he can ask only for actual losses- not imaginary 'consequential' losses. If, as you say, no service was lost, then the shopkeeper has no losses on which to ask for damages.
Since a suit has been filed, it's now up to the court to decide. The court will 'determine' the facts of the case, and decide accordingly. I say ... have some faith in the system; Judges don't like spurious claims, and are not idiots. I suspect the shopkeeper never intended to pay for the work, and is trying to bully his way through.
You can help by testifying as to what you saw, and repaired. Youmight also direct your friend to whatever standards youcan find that might have required bollards, or other protection,for that pipe. A little detail like that just might give the judge the hook he needs to hang the shopkeeper.
