Pond5 should start to include keywording services for free. Keywording should not be a contributor's job. Not all contributors are English native speakers: I often have troubles to find specific names for certain actions which are totally different in each language. For example, in Romanian, we do not have things like "air quotes" and I had to research two days to find the right expression. A non-contributor keyworder would be much more neutral and correct.
The best solution would be to let the contributor add whatever he/she thinks is necessary(but not mandatory) and have a pro keyworder do the final job, i.e. add the right title, description and keywords.