I recently began mailing tax delinquents. Originally I began sending yellowletters. I have found that yellow letters give a high response rate, but the callers calling in from this mail piece seem to be more curious than anything. They often call asking who I am, and why i think their house is for sale. I also received quite a bit of calls asking us to remove them from our mailing list. I have now switched to a simple short post card that says I buy houses in any condition, and lists the benefits I can offer (cash, quick closing, no commissions, etc). The response rate has decreased compared to the yellow letters, but the callers that call from my postcards are solid leads actually looking to sell a property. The curious tire kicker calls have decreased. I'm still testing both, but as of now I feel the postcard is a better route for me in my market. Real estate is local so I advise you test both in your market and see what works better for you.