For an exchange, they want your intent to be that you hold the property for long-term business or investment use (for both the property you sell and the property you buy).  

The study identifies with forensic engineering detail the immediate Bonus Depreciation 5, 7 and 15-year personal property class lives qualifying portions of a building that are normally buried in 27.5 year residential or 39 year commercial categories.There is the obvious benefit of accelerating the depreciation, shortening the recovery period.

do you sell the duplex to pay off the mortgage or what do you do?

I have seen a lot of flips in my neighborhood and the surrounding communities, but some are taking a while to sell as many are priced significantly higher than the median home values on blocks that just aren't there yet.

Don't get scared by the legalese or the crazy attorneys trying to sell something.

Not sure if I should sell and lose the awesome interest rate, or rent to get about $700/mo cash flow from this one property. 

Searching through past forums, some people say hold because it's the Bay Area (near Tesla and Facebook), while others recommend selling.

I’m thinking of selling the property7.

Why else would they sell so cheap?

Its much better for them to sell a high dollar house to a retail buyer.