Like @Kyle Mccaw noted there is significant value in goodwill and I imagine you profited nicely over this pleasant long term relationship. 

When you live in that duplex for 2 years and then sell you'll be able to take 50% of the profit tax free (the allocation for the side you lived in). 

Additionally, keep in mind if you do this in a Roth then there are NO taxes on the appreciation, rental income or profits when the Roth liquidates the asset. 

The $10,000 yearly maintenance fee is really hurting your cash flow, as it’s eating up all your profits.

Make it a habit—underwrite one deal a day until you get the hang of it.The tougher part, and I think what you’re really asking, is how to turn solid underwriting into a profitable deal.

Sometimes making a smaller profit and providing value is far better than holding out for a bigger payday on a bad deal, I like that.

As I studied earlier, the first thing you should do is marketing, then get a call and do a property analysis to understand if it's profitable for you, then meet with the seller and sign all the necessary papers, then if there is a debt in the bank we do a reinstatement quote, then do a title search to check if there are any hidden debts, if everything is fine we look for an investor or flipper and sign an assignment of contract with him and wait for closing to get our money.

@Alex Hymanson  you should read the book...Storing Up Profits. 

83k profit Lessons learned?

After analyzing the potential ROI, we negotiated a fair price of $58,500, ensuring room for renovation costs and profit.