First off, thanks to the organizers for putting an enormous amount of work into creating this site!
The inclusion of "region" is already an enormous upgrade over CalGuns' marketplace listings. If you made it a step more granular by also having a field for "county" that would make the search filters very powerful and may be an effective way to represent the vastness of our state.
I feel conflicted about this. In some areas, counties are extremely large. If you live on the eastern edge of San Bernardino County, taking a trip to "Santa Barbara" (both are technically in Southern California!) is like a major expedition. And then there is always the joke that within LA, going anywhere (even to LA) takes at least one hour on the freeway at rush hour. On the other hand, I am in both Santa Cruz and Santa Clara counties nearly every day (we can literally lob a bullet into the neighboring county from my house, although that would be illegal), in Alameda County once or twice a week, and a trip to Monterey, San Benito, Contra Costa and San Mateo County happens typically once a month.
There is also the question of how important something is to me. Our two most recent vehicle purchases required 3-4 hour trips each way. I would drive that for a very desirable and unusual gun, and if I could get a great deal on something I really want, I would go to the other end of the state. On the other hand, for a Glock 19, I won't go more than two freeway exits, it's not worth the hassle.
I think the current policy of every listing showing the city is a good compromise. As the number of listings explodes, this may have to be revisited, but any solution will end up being complex, with things like distances (the way Craigslist does it).
You might also consider narrowing the firearms categories further beyond "handgun" and "long gun".
I'm with you on that. Separating pistols v. revolvers, and shotguns / traditional rifles / military- or black-style rifles would be a good start, if the number of listings gets unmanageable. But not too finely please, because it makes browsing too hard: There are many guns I like, and I might just look at all recent listings to see whether there is anything that particularly tickles my fancy, or is a great deal. Another example: if we separate by maker (Sig v. Springfield v. Wilson), by caliber, by model and clone (1911s are made by many companies, Cz clones include Tanfoglia, the Beretta 92 is cloned by a half dozen companies), then someone looking for a 9mm 1911 will either never find it, or have to look in a dozen places. So no complexity until it is needed.
I hope to see this project grow and succeed.
Hear, hear.