And you avoid things like damaged properties (guest insurance from airbnb or prop manager themselves cover that), evictions, collections, etc.   

What are some pros that I can highlight from the seller’s perspective.Here are a few that I’ve come up with:1) monthly income at a higher interest rate;2) avoiding a larger tax bill by reducing the purchase price (on paper);3) a promissory note that they could potentially sell down the road.Any other major ones I am missing?

I wouldn't mess with your index funds if you can avoid it. 

I tried to set up quickbooks online, but without paying $720 a year for the ability to do class tracking, it seems like it wouldn't be as beneficial.I know there are other tools out there more geared towards real estate like xero, etc, but I'm still trying to avoid paying so much every month.Has anybody used realtyzam or rentalhero (rentalhero.io) they seem to be linked? 

I don't know of a way to avoid that if that's the data format they want to use. 

That said, I completely understand your concern about deals looking "too good to be true" when you’re putting in 50% down.To avoid this, it’s best to analyze properties as if you were using more traditional financing (20-25% down).

Now that doesn't mean you can't get creative on your own to avoid paying retail. 

Auctions are quite possibly the worst place to buy if you want to avoid repairs.

Since you mentioned a construction site injury in your initial post, the best way to proactively avoid premises liability claims is by keeping a clean worksite.

Use a promissory note drafted by an attorney to outline loan terms, including an interest rate that aligns with IRS Applicable Federal Rates to avoid gift tax issues.