I'm completing a Rental Calculator query form for a potential rental sale property and just wanted to know how does one come up with and determine the percentages for the monthly landlord expenses paid portion?

This portfolio consists of both my own properties held by my business as well as properties under our management owned by other entities and individuals.  

When dealing with individual sellers, the most important thing is their motivation. 

There is a tax form (W7) they need to complete to get them a ITIN (Individual Taxpayer Identification Number) for tax purposes since they don't have a SS #.......but that can be done after they invest and before tax returns are filed by the partnership.  

Or are they typically sold individually?

As others have mentioned, learn the fundamentals and analyze each property individually.

Keep in mind that each individual property has different utility bills (due to energy efficiency, possible water leaks, square footage, number of tenants, etc)  Calling the utility company will at least give you a starting point. 

I have called several individuals in San Antonio from homes I have found in Craigslist but so far I have not been able to pin a house down. 

I'd like to connect with anybody on here, and especially the individuals from San Antonio and nearby areas.

I would love to network with other individuals around the area that understand creative real estate investing & other wholesalers as well.