I hired a GC to manage the build out, but there has been no consensus on who is responsible for the utility payments (Water and Energy). 

Are you utilizing REPS?

If the property is sub-metered/ if you intend to have the tenants pay utilities make sure to mention that to them. 

It now cash flows beautifully, which I continue to utilize for other my other properties. 

The thinking on this is that although the buyer utilizes what appears to be a purchase contract, it is actually being used as a purchase OPTION, and as such an option contract which clarifies that the purchaser is actually obtaining an option to buy should be used.   

They need to do all their due diligence including understanding the value that will be added by the ADU, the finance options available, the consequences of adding the ADU (rent control, property taxes, rental limitations, etc), etc.Good luck As with all things, it depends on the investor and the equity.If they are able to leverage existing equity to buy it under a HEL or HELOC, then they are adding equity with no out of pocket expenses, and adding immediate and longterm cashflow to existing stock.We like ADU's because there isn't more land being created in our city that is landlocked...but there is more density available to those with large lot under-utilized sfh.In my market, it typically costs $2 to add less than $1 of value on single build ADUs.  

We want to travel and invest and are considering converting this short term rental to a long term rental to avoid sales tax, paying utilities and general management of the property. 

The other half of the accounting records is coming from online purchases, utility payments, etc etc where they are sending you an email. 

I pay no utilities and these are all one year leases.2) THEIR CREDIT RATINGCollege students almost always pay their rent.

Most investor utilize short term hard money debt to scale their flipping operations where the lender will fund 80+% of the purchase price and the rehab budget which can allow investors to work on multiple projects at once.