In multifamily deals, I've seen a flat "guarantor's fee" paid to a partner who is brought in for the sole purpose of signing on the loan and bringing their personal balance sheet to the deal to satisfy the lender's underwriting requirements.  

In some markets, supply remains very low, and prices continue to creep up with demand.

I have to say there is something satisfying about customizing your tracking tools to be exactly what you want, but I am LOVING the fact that I now get automatic reporting just from doing my books, which I have to do anyway. 

I am also curious to understand as how can one person can grow their RE investment if his/hers salary remains constant. i.e if someone is making 100k and has a mortgage and rentals, at some point in time the bank would not be able to finance the loan for a new rental.

I've met them all already while doing work on the house to satisfy the inspector's requirements.

If I am pre-approved for a 200k home but If decide to buy a duplex worth 150k would I be able to use the remaining 50k for some TLC.2.

In a sandwich lease, the investor remains involved and on the hook as a principal lesee/optionee throughout the lease term.

Do I need to look at getting the seller to finance the down payment and then see if a bank will finance the remaining 80%? 

That means you need to have 25% remaining in equity. 

I just used @Daniel Hyman and am really satisfied.