What Are The Best Ways To Size-Up A Prospect?

Making a list of unoffensive techniques.
Best = Most informative / least detectable
Example: You get a lead for some work but have little information about them before your first contact. What steps do you take before, during, and after your initial visit, to categorize the prospect in terms of their discretionary financial resources?
<ol>
<li>Google Maps - street view </li>
<li>Zillow</li>
<li>Number/make of vehicles</li>
<li>Drive by </li>
<li>Public database info</li>
<li>Ask them where they work/live</li>
<li>Age</li>
<li>How they dress</li>
<li>Grill the referrer</li>
</ol>
Others?