500px is a big fat pile of *.
nobody is buying anything there, it's just a bunch of snotty amateurs using HDR and top notch gear and then telling each other how good and uber skilled they all are.
it's a F joke, just like Flickr but a lot worse, they really take themselves too seriously, there's people there spending 20K on camera gear without having ever sold a single photo for half a dollar !
in plus, no watermarks, big images ready to be grabbed away by freeloaders, and low prices in case some fools even goes as far as wanting to buy a print.
it's the same stuff you see on photo contests, and guess what it's usually the same stuff that hardly ever sell on stock and even in art galleries .. typical "academic" stuff ! looking good but not good enough to be sold.