And you would get to indefinitely defer all tax on the gain from the sale.

Again with tax auctions, some kinds of tax auctions are referred to as a "free & clear" sale.

With everything paid off, they’re looking to slow down but are hesitant to sell due to capital gains considerations.Purchase Price: $1,750,000.00Downpayment: $400,000.00 - Will do a 1031 - Selling two of my SF properties for the downpayment (bought for 120k + 146k back in 2017 & 2015). 

I am adding about 20 more this year, but there's one small pocket I'm struggling with the financing on (honestly, due to Huntington Bank dragging their feet on items, etc.), so I'm seeing what other options there may be. 

That's 50k a year gone and you are losing tax write-offs and equity potential.

What if they build just outside the city limits, so they are not paying city taxes?     

Is there anything specific I should focus on during the due diligence process, particularly regarding title and document inspection, compared to a traditional sale?

If you can come in and operate effectively I think you'll find success rather quickly due to that.BTW - for a property management platform I would highly recommend Buildium.

There are rentals, fix and flippers, lenders, tax liens, note investors, STR, commercial etc.

Positives are proximity, low property taxes, no income taxes, no weather events, very low maintenance stucco/tile structures, “young” properties (5-20 years old)