I just noticed one of the rudest rejection reasons there is: "image overpriced for this category". Around 5-6 rejected for being overpriced (20$ + allow resizing / EPS vectors).
It's acceptable that FP targets "budget buyers" or that these particular images could be deemed unsuitable for this price rank, but that's mostly a decision the submitter has to take and an agency like FP that allows pricing options should NOT interfere with his choices. A big minus for such a cosy upload-friendly site. I might stop uploading at all (well, it's not that payouts are frequent anyways).
p.s.: I tried pricing vectors lower on FP (considerably lower - if I'm not wrong around 5$) but the sales were ridiculous. Web resolutions for pennies... not my cup of tea where there is no quantity factors making up for it.
p.p.s.: Here's a sample of one of the rejected images:

Of course it's not about the rejection per se, but the manner and reason for it.