What's the price tag for keywording.?..
In general: 2-4$, 2 for series. Title/description included.
They never will post it in public.
As you know, I'm into outsourcing now and I had thoughts about a similar service at a place where the wages are 35% under those of Chennai. But to be perfect and microstock-relevant, I should check all the output myself plus check competing shots at the sites to bump over them as to relevancy. Given that overhead plus the costs (included training) a price of 3$ is realistic.
Personally I would never let go the metadata out of my hand, since the right wording is vital for correct search info placement. It might make sense for volume uploaders though and image "factories" that run a tight shop.
The least the keywording services should do is put some examples online to have a quick idea of the wording quality.