How do you "buy right"?

[Charles Benkendorf]

Hi all, I was reading some articles from Brendan Turner about buying right - how he looks to buy property at 70/80% of the value

If you follow this rule, what are some rules of thumb you use to identify these opportunities?  Here are a few scenarios I'm thinking of:
1) being sold by a realtor - price is likely close to market value. a notable exception is if house needs significant work, in which case the cost is being accounted for in a lower price.  It's possible with a longer time on market, they may be open to a lower price.

2) being sold by owner - may be more opportunity here. price may be over/under market value.

3) foreclosure - bank is motivated to sell. may be willing to sell under value especially in a slow area.

based on this, it seems like best bet would be to pursue houses sold by owner, foreclosures, and listings that have been on market for a while. 

there also is a whole other approach of finding motivated sellers - drive bys, bandit signs, etc.  But I'm not ready to get into that yet.

Thanks!