There's furthermore a magnificent chance that any gesture you make with a book about home maintenance will be interpreted as an undercover effort to tell your tenant that they're on their own if something goes wrong and not to call you.

Even though your cleaner didn't ask for extra compensation it will be a nice gesture on your part and they will appreciate it. 

I don't think you need to pay him anything for his time spent putting together a bid (sounds more of a guilt ridden gesture, although nice, no one turns down free money).

It is also possible that the neighbor could file a suit against your mom and seek a court order to remove the fence, that would require your mom to defend herself in court by claiming the land under the California adverse possession statute.Alternatively, you could advise the neighbor that your mom has the right to claim the property -but as a gesture of good faith, offer the neighbor an amount you feel appropriate in exchange for the neighbor deeding the disputed portion to your mom. 

A contractor that you know and trust with no history of such things is another story, where I would probably just let the contractor know I'd made a note of it and was giving them the benefit of the doubt based on their clean history - further explaining to them that I had to take that action/stance as a gesture to the tenant, and that I value their service.

Might be a nice gesture plus another good reason to visit and look around.

@Jay HinrichsVery nice gesture. 

I think that would be appropriate and be a good will gesture.

I really appreciate the kind gesture.

Small gestures like this really encapsulate the care that both Jake and Gino have for their students.