As to the double payment and muddy waters, not your problem.

Sometimes I get surprised by what they tell me so I double check.

First time I've heard of this method but certainly sounds creative - The end buyer is probably likely to still come up with close to $100k on transaction costs with the double dipping of loans and other processing fees most likely. 

Studs, plates etc are probably double. if they have the electric and moving the HVAC(duct) in the labor it's potentially not a bad number.

If not you’ve doubled the benefit of a new loan. 

Double in five years.

Would it just be a double close to pay off the seller financing and I walk away with the appreciation and cash flow earned while under my control?

Basically, 24 different properties spread across 3 Florida counties will need to close all at once during one closing.My thought is to do a quasi-double close/bridge loan where I bring in a partner to fund the deal (about $5 million), and then have separate closings as quickly as possible after the fact in which we sell the other properties we don't want. 

It's no different than any other deal using other people's money (private money, hard money, etc) which I would imagine falls under this category you do not endorse.I've bought many things with credit (cards or loans, all the same to me) and flipped them for double or triple what they cost me.

The Rule of 72 calculates the time it takes to double your investment.