I don't think you can use PQ at all, especially if you're going to base it on what stock agencies want.

Yes, a camera might be able to produce images of a good enough quality.

BUT, can the photographer say the same? There's loads of talk on the Alamy related forums at the moment (mainly by one woman) about the QC procedures there and how her images keep failing. Although she won't admit it, in the photos that she's shown it's quite easy to see why she has failed QC so many times.