How do I determine what percentage of the profit for a product I developed should be mine and how much should be the jobber's?
I was planning to sell my product myself until a jobber asked me to sell 500 pieces to him for his catalog sales.
Standard margins depend on your industry. Find this out before you go further. If you don't know, call some other catalog vendors of similar products and see what they're doing.
Do you have somebody in your industry you can ask? Somebody with specific experience in this product area? If not, do a web search, and find somebody.