Ask HN : commission rate for business intermediaries selling SAAS

Hi, i'm slowly deploying my b2b SAAS, and am waiting for my first customer. One business intermediary found a potential customer, but he is asking for a 50% commission on the sale. I find that extremely excessive and don't want to start the business relationship with that salesperson on that basis. How much do you think I should ask (please, answer only if you'v had a similar experience) ?

The contract would bring about 500$ a month total for a start, and may end up reaching twice that amount in the future (not much more).