Ask HN: How can I find out what firms like ad.ly are charging?

I'm interested in launching a start-up that is involved in social media marketing which is a little similar to companies like ad.ly. My problem is I can't find out how much businesses in this industry charge for commission per campaign. I also don't know how they take their commission out.

For example, let's say a client used $20,000 worth of their services and their commission percentage is 10%. Would they add $2,000 to the $20,000 total making the final fee $22,000 or deduct their $2,000 fee from the original?

I know this isn't really Hacker related stuff, but I've been researching for days to find these answers and I've come up empty and HN is one of the smartest communities I'm apart of.

Thank you.