A company that I am associated with, Renovation Funders, has a great program that matches you up with a project, and when that project is completed, you get paid your investment back plus a percentage of the selling price after the property sells.

Each individual should have a percentage commensurate to the amount of value they bring to the table. 

@Cashmere Robinson Great point on looking for a distressed property to add instant equity with the work put into the property.Account Closed Thanks for the advice and good points to consider.

Be aware of the acceleration clause in her mortgage.Offer to lease the property with an option to buy, give her an option payment or monthly option payments that apply to the balance (this represent a no interest loan)Buy it at a great discount and offer her a percentage of the net profits when the property is sold (after you force the appreciation) at an agreed time of 3-5 years.

The financing is usually at a higher percentage rate and usually for only several years.Example: You buy a mobile home in a park for 3k.

Way too many variables in this type of transaction, would have to know your entire individual and corporate tax situation, For example, depends on your percentage of ownership before and after the transfer, your bases in the property vs. it FMV on date of transfer, and a bunch of other information.  

They may be more amenable to a flat fee plus a lower percentage - at the very least it's an alternative that helps you offer options that still cover costs.I have to say, I can't recall seeing anything as low as 2% for the buyers agent in my market; the lowest I've taken is 2.7 but the lowest listing I remember running across were 2.5.

Further, the large discrepancy causing some homeowners' tax assessments to date back to 30 years ago is because of Prop 13 that protects older, long-time homeowners from higher tax assessments/ tax payments in CA (it limits the increase on tax assessments to a certain percentage of the previous year unless the property changes ownership, at which point the tax assessed value is updated within 12 mos of the close usually). 

What percentage would be the highest acceptable?

Even if the person is there 1 day a month your ex-owner will expect that he only pays X percentage of the utilities based on square feet.