How to manage advertisers?

I’ve been approached by a company/website that want to advertise on my site and they’ve said they are willing to pay me $20 for every 1000 hits.
My question is how do I go about tracking a 1000 impressions/hits and giving them some sort of access so they know I’m not making up the numbers as I go along.
Any help would be much appreciated

See original post by szkoda