Getting more energy efficient can also help your cause if you are paying utilities.

Read section 21 of the CA Residential Purchase Agreement (assuming you transacting on this document).I've not been through mediation or arbitration myself, but if the buyer removed all contingencies when he submitted the offer, then cancelled, AND you suffered actual damages (a subsequently reduced sale price), your case seems pretty iron-clad to me.I believe you can enter mediation and arbitration without a lawyer, so I say go for it!

I have been listening to your podcasts every single day and it gives me a lot of energy, motivation and knowledge.I was wondering, are there any folks from Europe here as well? 

Things happen, and there will not be a refund if the sale is cancelled for something like a bankruptcy.Check for any government loans against the house for construction type of projects, there were some energy related ones a few years back. 

I’m looking for lights that are energy efficient, so maybe motion sensor and that aren’t an eyesore

The advantage of electric cars is you can use renewable energy or nuclear power generation methods.

And the insulation issue, that's an energy code thing.  

You'll be surprised what some Sellers will accept in exchange for reduced taxes and a steady income;2.

.- Niche Knowledge: (STR rules, ADU's, Zoning Expertise, down payment assistance programs, AFH, Opportunity Zones, etc)- Discounting: (If you are new you could always discount your services to add value (reduced commission for brokers, lower management fee, reduced fees for JV's).- Superior Service: Somewhat counterintuitively you can actually add more value despite being new.

At any rate if you have a bad feeling about this couple (and the "money business" of the boyfriend plus what sounds like 3 high energy children ready to wreck your house would worry me more) then find a way not to continue with their application process.