I have found more machines at yardsales by asking if they have any sewing machines or sewing machine parts, than I have from seeing them in the sale. Many times they think that the yardsale crowd probably won't be interested in a danged ole sewing machine or parts, and they have all of the other stuff to get out for the sale (interrupted by the "early birds" of course), so they either don't bring the machine out at all, or they finally get around to it later in the morning. Way to go!
CD in Oklahoma