MicrostockGroup

it is difficult in the sense that you must choose categories and tick a lot of boxes on site to complete submissions

but IPTC keywords should import correctly - no problems for me

Submission is timeconsuming. Recently I found out that reviewers cannot read the description from the metadata. So if there is information of any importance for the editors or for the buyers you do better to add that in the 'message to image editors' section. Information about how the image is made (long exposure, shallow dof...) helps also. Otherwise you often have to redo submissions from the red/green section.