Rules of thumb / Heuristics to know if it's a truly true "Deal"

[Kumar Tummalapalli]

What uncommon "rules of thumb" / heuristics do you use to decide if it's a real "deal " ?  

The ones I use : ( these are not uncommon though :-) )

1. AVM like zillow / realtor and so on

2. Tax Assessed Value ( know the equalization factor for your county ) - and when was this assessed ?

3. A very similar comp on the same street or of it's a condo ( Full comp analysis is always there but that's more time taking and sometimes with the same comps - diff analysts arrive at diff prices)

4. Keywords from description such as "investor special" and so on