The only good use I can see of the fees are based on rent charged would be for a tenant to purchase it and charge themselves $0 or near $0 rent to avoid the rent based charges. 

So it became a long-term action of repeating that cycle to achieve decent LT tenancy base. 

If it were to read LP member owns XYZ% and will receive a certain percentage of proceeds based on property performance, that's a different story.

Real estate's "gross rent multiplier" is Wall Street's "sales to revenue",  "cap rate" is roughly "P/E ratio".When evaluating markets and investments I tend to start with GRM (or lazily the 1% rule), then attempt to return a cap rate based on assumptions about costs, then I work my way to multiple years of projections (assumptions about inflation, amortization, tax benefits, etc), and if I am partnering with one of my smart friends I have to pull up an IRR (internal rate of return).I also look at regional employment levels, median income to rent ratio in the zip code etc. 

It seems most commercial lenders base loan amounts on rental income rather than the property’s value.

We don’t do overseas rental units but recently have traveled in those countries and my brother bought in Italy and my son is based in Sicily.  

Since you have no contract, there is nothing that says you do not have to pay if you are not satisfied, and your spreadsheet would seem to indicate you owe him the money.Similarly, since you paid him for previous work on the spreadsheet, and the spreadsheet shows you owe him for additional work, your argument is not very strong.

All my rentals are never less then 15 - 20% net based on cash purchase.  

Great post, I already here people making major changes to their strategy based on the incoming administration as it relates to not only taxes but other proposals either discussed or used as scare tactics.

Unfortunately, based on my experience, I'd be surprised if this is a legitimate opportunity for investment... more likely it is a means by which Eric and his team gets rid of properties they no longer want.