This wasn't some clever trick was it?

And not because you are not clever, think  outside of the box enough.. does it magically or suddenly mean that an inferior method is suddenly not inferior.

However, if I was soliciting a professional service, yellow letters and other clever direct response pieces don't come across as particularly professional, IMHO.

For that, you'll need your parents to sign for you, even then that can be sticky on who the contract binds.But honestly, do what @Doug Pretorius recommends (which is very clever), or better yet, do what my boy Gary Vaynerchuk preaches and learn to have micro-speed and macro-patients. 

Typed on 28 pound linen paper, logo on both envelope and letters.

Now, if I had basically the same MESSAGE on both letters and postcards, I might still get more calls from letters, but it won't be twice as many calls compared to postcards.And one last point, clever direct marketers mix up the media - maybe mixing letters and postcards over the course of a campaign, or (as we do) using different postcards - perhaps several in a series, or some with photos of houses, others with photos of people, etc.  

If that is it, it seems extreme to go from "he's a clever investor that deserves admiration" to "he's scum".

Such as services offered by @Jerry Puckett or Clever Investor.That brings me to post direct mail.

Some beautiful antique linens that I use regularly.

Anything clever about it?