You ignore the DNC at your peril, once I got 2 demand letters in the same month I paid them and decided to take it seriously.

I have $100k in appreciation to date.

I'm not sure you are going to be able to find a property for $100,000 to sell to an end-user at $170,000 with $40,000k in work from afar. 

@Roy Loganeither1. your own direct marketing to property owners, or 2. through someone else (a wholesaler, another investor, your network, your uncle's neighbor who wants to sell their house and doesn't want to list it and tells your uncle)

Additional things to consider: where is the breaker box and do both units have access to it if needed?

Mostly house flipping community, but will be  relevant to others.

This is a terrible way to price a property.

They are thinking they want to stay there at least 10 years, so they want to buy it and asked the best way.

My target purchase price is no more than $410K, aiming for an ARV in the $530K to $570K range.I'm comfortable with small to medium-sized renovations that don't require major structural changes or additional square footage.

All that's due is the security deposit, for you to return as long as no damages to the property.