comission contract on sales

I am looking for a freelancer to create a commissions contract for sales. The commission structure I have in mind is a fixed commission per sale. I also have a specific target goal in mind that needs to be met within a duration of less than 6 months. I would like the target sales goal to be clearly outlined in the contract and specified certain clauses. Additionally, there should be a clear benchmark on how to gauge success and how to assess performance in achieving the final goal. I am looking for someone that is detail oriented and experienced in creating such documents.