Handwritten adds sincerity and authenticity.

The relationship was probably not real, authentic, and/or strong in the first place.

There are standard postage sticky stamps which still give your mailing that authentic feel and look.

When it comes to direct mailing and sending out post cards, what are good authentic ways to attract a motivated seller to call you?

That is a really unique authentic angle. 

Bob find a different attorney.There are attorneys who only know about vanilla real estate deals and transactions.Then there are attorneys who specialize in business transactions and also exotic structures and owner finance strategies.Clearly you either explained what you were doing to them in a wrong way or they do not have the knowledge to make an accurate statement.One of my pet peeves is people answering a question when they do not know the answer and "winging it" to make themselves look better.I find more power in telling people I do not know but I will try and find out.You can't know everything but you can spend your life trying to improve and be authentic.

Authentic.

See here:  FCC to require phone carriers to authenticate calls by 2021If you use something like Callrail for tracking purposes and use their numbers for cold calling they are now showing up as "Spam Risk" on caller ID which has dropped the contact rate significantly. 

Thank you for being authentic in your response. and congrats on creating a new business. 

Actually handwriting the letters yourself will definitely get you a better response rate, as it feels more personal and authentic (because it is!).