That's literally what I'm trying to avoid, and I have faith in the BP community that a better solution is out there!

It’s hard to juggle and blend good faith duties, fiduciary duties, best practices all while trying to carve out as much profit as possible for #1.

Like anything in life- some guests are fantastic people and renew my faith in the STR system as well as humanity, some seem like they are from another planet and have insane expectations.

Again, I have no doubt that your intentions are above board, but you should recognize that this decision should have been made before the seller tied up the property under contract with you in good faith that the agreement would be honored, and I would suggest that the risks of your understandable oversight should be borne by you, and not by the seller through a renegotiation of terms this far into the process.

I am a Project Manager in the Video Games industry.Recently, I've been really studying and focusing on my long term future (retirement) plan, and I believe Real Estate Investing is a great way to achieve that, so I would like to learn as much as possible from this amazing community and, eventually, take a leap of faith to get started.Since I currently have a Full Time Job that is really demanding (~50 - 60 hours a week), my goal is to try to create a passive income from my investments.Looking forward to learning from all of you!

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. 

or invested in mutual funds which they have lost faith in and/or scare them because of the risk.

I have been taking it on faith that $171/foot or $26/foot are quite possible. 

I have a Toro and it's been faithful for 5 or so years with just standard maintenance, though I'm doing several driveways vs an entire parking lot. 

I put Zero faith in Zestimates.