If there's a geocodable address in the optional location field, we use that. If not, it will default to the general region it's posted in.

We're currently seeing approx 75% of listings geocoding correctly, but like you said the resolution is often low. In order to change that, we'd need at minimum cross-street level data from Craig. And although I've talked to him about it, I don't think I have enough leverage to change this without a user outcry..