I had specifically asked for numbers including mortgage payments and they emailed to me.

You likely only made a down payment of 3-20% ....but you still get to write it off on the full value across 27.5 years.So 400k/27.5 = 14,000 ish a year of a write off where during the year you didn't need to incur an actual expense, no cash outflow. 

For some buyers it would end up being less than a 2.5-3% commish, and for others more.The tricky part for the buyer is it would have to come out of their pocket in addition to the down payment, whereas a commission paid by the seller at closing is included in the purchase price and absorbed into their loan (usually unless paying cash obviously) so the buyer only has to make the down payment out of pocket.

You can take out home equity loan and use that as a down payment on an investment property, but I'm pretty sure your return will be very poor.

Have you considered tapping into your existing rental equity for the down payment?

Gave me the monthly payment and I checked it against a mortgage calculator and it's exactly what that said. 

Create the payment that’s very low in comparison to what your keeper would bring in rent.  

Then the rents would cover that payment plus the mortgage with cash left over.

To improve cash flow, consider a higher down payment, mid-term rentals, or renting by the room.

But why would that make them want to use this financing method?