As you already know, the quality of the investor agent will speed up your learning curve, and save you money, time, and headaches. 

The money will follow that.

You didn't make any money over the 10 years you owned it?

Due to the confusion on their end and their slow response, it's costing me more money than if I just went directly with the vendor from the start.

There are multiple billion dollar companies dumping money into the city, such as Intel, Google, Honda, and Amazon.

It normally doesn't cost you any money to open and to be able to access that large amount of equity to buy or stabalize your current portfolio allows you so much more opportunity costs.For instance, I took a $200K LOC out on my primary residence when I first started in real estate.

This is what blows my mind about the cults of seller finance - they teach you to pay anything for a home because you can put little money into it.

But if you have to jump through hoops or spend a significant amount of money to put it in might not be worth it. 

As far as benefit to the seller goes, @Matthew Paul I think you are probably right on the money and regardless of whether they would have preferred to stay in this house rather than move, it is likely providing them some excellent cash flow; and I'd be hard-pressed to come up with a deal that serves both parties better than the current situation. 

Always have rent money coming in from the duplex vs SFH (not).2.