There are the shops like Komehyo which specialize in use luxury brands and those such as say, Book Off, which specialize in well, all sorts of stuff.

I believe part of it is being able to get rid of stuff easily while not having a guilty conscience about throwing away something that was quite expensive. Rules for disposal are also an issue - I've given away random things at work just because it was easier than potentially running afoul of garbage rules, plus I wouldn't feel bad about it.