Say if you want to have a directory like dmoz, yahoo, google etc but would be paid like yahoo. How much would you pay your editors? Would you pay a percentage of the sale of a flat fee/link
It should most probably depend on the work done (accepting/rejecting) links as opposed to the submissions recvd. 50% sounds a good deal.. but you should take into account ur marketing expenses as well so 30% a fair deal IMO.
Uhm if you charge like Yahoo 50% is way too much... $10 per reviewed submission would make anyone happy and thats not even 10% of the yahoo price.