So I'm bringing a product to market...what happens now?

I've made the formulation, I'm paying for the manufacturing, and in just a couple of weeks, I'm going to have inventory! As soon as my samples come in, I'm hitting the road: going to nearby retailers to try to get them to carry my product.

How will that work? Will I leave them the product and invoice them? Will they try to negotiate the price? Will they pay me up front for the stock? Should I carry around contracts or receipts or...what? How does this work?