Bad estimate trick - playing people off of each other

[This was originally posted at http://timstall.dotnetdevelopersjournal.com/bad_estimate_trick__playing_people_off_of_each_other.htm]

One estimating technique I occasionally saw in consulting, which I thought was pathetic, is as follows:

The consultant faces a domain-specific problem that they're not familiar with (say writing reports, or doing some database optimization, or wiring up a backend service). So, they intend to sub-contract it out. They interview two separate contractors, and ask each for an estimate. The consultant, in their sneaky mind, figures that they'll play the two contractors off of each other to get the "real estimate", and whichever estimate is lower must be the honest and correct one.

The biggest mistake I see here is the bias that whatever is lower is more correct. Developers are notorious for low-balling estimates (especially if the manager demands a low estimate in order for the developer to continue), so this is historically a bad bias. It's just as likely, or more likely, that the higher estimate is actually closer to the truth.

I think a much better approach is to find a way to determine who the more reliable and experienced developer is, and go with their estimate, even if it's the higher one.