The 500px marketplace (where they license images as stock) is open to anyone, but for an image to be selected for Prime is an editor's decision, not yours.

They appear to be changing things to emphasize paid services - see this recent change - but you can upload photos there at no charge and skip all the extras. They used to have a limit of files per week for free accounts, but I'm not sure if that's still there.

Pricing is higher for Prime - if your work is selected. Bear in mind the royalty rate is only 30% unless you make the file exclusive

https://support.500px.com/hc/en-us/articles/207423197-Prime-and-Core-Collection-Prices

And the have a KOOK running the joint...modeling it after greedy Getty/Istock.  I pulled all my underwater work off there after he cut commissions from like 60-80% to 30%.

Dropping commisions from 60-80% to 30% definitely sucks but isn't 30% about the average for current microstocks?  Maybe even a bit on the higher end commission - again, for microstocks.

500px prices aren't really microstock prices - more like Alamy but without the sales volume Alamy pays 50% (if you opt out of distributor sales, which I have).

I'm not wedded to any particular percentage - if an agency spends a bunch on marketing and promotion and can deliver a huge volume of customers, even 20% can be a good deal (see iStock and Getty back before they started circling the bowl). 500px is a newbie agency with no track record (with respect to sales; there are certainly some gorgeous pictures at 500px) and before they could even get a track record, they cut the royalties back from 70%.

I couldn't say if it was hiring KK Thompson or cutting the royalties that was the primary motivator for me to remove my stuff from marketplace (I left the files there in case they came to their senses at some point), but I was no longer interested in what they were doing. The fact that they have now upped their fees and are trying to flog directory, web site and promotional services suggests they're now hoping that will be their way of making money versus being an agency. That's not useful or interesting to me.

Dropping commisions from 60-80% to 30% definitely sucks but isn't 30% about the average for current microstocks?  Maybe even a bit on the higher end commission - again, for microstocks.

They are not a micro stock company, but their leadership is from micro stock.