In this case, it is probably best for them to list with an agent instead of sell to you.When you recognize this, refer them to your real estate agent and have them list their property.

when you don't turn in a list your exchange dies at day 46, you get your proceeds back and your gain is recognized. 

You can definitely do this yourself, but recognize that there's a risk associated with doing so. 

It seems like a big gamble to guess at which option is more secure.

A couple of questions on the calculations (I've been using this calculator). 1) I assume the recognized gain is the change in equity + debt? 

If the second unit does not have its own electric meter it should still work (worked for us,  we bought a home with attached apartment with our daughter who was a college student) also if the appraiser classifies the second unit as an accessory apartment or mother in law unit or casita instead of calling it a "duplex"   We're taking a gamble on a property right now where the underwriter said he believes the appraiser will be classify it as a single family with accessory unit (fingers crossed) this property is two separate homes with separate meters, so there's a chance appraiser will say the dreaded "duplex" and we wont qualify. 

I'm starting to get a handle on recognizing bad deals but am curious what kind of criteria y'all use for weeding out and getting to the more attractive stuff.

Additionally, a Series LLC that had a presence in California (which does not recognize the Series LLC) and was subject to the $800 annual LLC tax for each series.  

The possibility of an error that could cost tens of thousands is not worth gambling.  

I'm willing to accept some risk, but I'm not going to gamble.