Of course, anyone who follows the above advice is likely selling to DomBuyer cheap (thus one of the motivations for the posts, as you're doing all the work finding the gems for him).
The way to get the best price isn't to flip it fast.
Also, if you actually try the above, factor in the value of your time. It might take 500 emails/calls to domain owners to get one deal done. If it was so easy, DomBuyer would just hire staff.
But, it's time consuming (I know first-hand), so when you end up calculating your hourly wage, that job at McDonald's starts looking good.
You're also competing against automated bots (anyone who owns domains knows they get MANY emails per month with lowball offers, because folks are scripting the Overture tool and matching it up against the WHOIS database). Those bots can search for names faster than you can.
Conclusion: All the "easy" money has already been made, years ago. The business is fairly mature now, and the returns on investment are approaching "normal" returns of other businesses. Except when buying from newbies (like folks in "awe" of the post!).