Once you know what a buyer(s) want, decide on one marketing technique and again become the expert at that marketing technique.

Author and investor @Chad Carson used the techniques and systems outlined in his book to retire at age 37.

Your plan provider can confirm whether or not it matters as a duplex.One technique for starting investing is staying as a renter and taking advantage of primary residence financing and other benefits, just like your potential duplex here (15 year 401k loan, easy insurance, FHA loan, etc.) and then you do something similar again with property #2 (even if you don't plan to leave property #1).  

We do have a deal that she can only use them for educational purposes until she is fully finished, then it's up to her to decide.The other advantage of this technique is that she is learning the business, both in having to get her hands dirty in the rehab and cleanup (TOTALLY what a 12/13 yo loves...not) , and now in following the financials of managing a rental.  

To be honest I wouldn't recommend doing things you may hear on the podcast like letters just because its just because the technique is really over-saturated in the greater Boston Area.

I'm still in beta and am redoing this exercise now as a retiree.A couple of techniques I used back then: Tony Robbins sold the cassette tapes Unlimited Power that helped me identify and prioritize my short, medium, and long term goals.

I'm currently marketing for off market deals through direct mail and other various marketing techniques. 

Not sure if it is technique or it is just thinner. 

One such technique is to "answer their question with a question", after giving them a brief statement.

MLS is the way to go, how you decide to use it and who you use it with make all the difference.I do, however, agree with all the other selling techniques you've mentioned.