I live in Portland, too, and the competition for vintage at estate sales is ferocious. Portland has more vintage clothing shops per capita than any city in the U.S. Of course it's great if you're a shopper for vintage to wear, but it can be grim if you're a dealer looking for vintage to resell.
Of course there are other ways to buy than at estate sales, so one has to learn the ropes of more direct buying methods. But it's a challenge here, that's for sure! But it's also really nice living in a town where you see kids walking around in vintage as a matter of course. Or where I can wear any of my vintage winter coats and get admiring comments instead of people looking askance.