You should be able to track every order that is placed even if you don't collect the customer's money. There are many systems to track your sales. I prefer to have the leads and sales come directly through me whenever possible. You can buy products at a large discount through a wholesaler. Just order the products from your wholesaler and mark them up.
Some companies sell licenses to reprint or duplicate their products.
You determine the price and keep the profits once you pay for a license. Costs vary from business to business. Affiliate Programs Affiliate Programs are the most common way to acquire products to sell cheaply. You sign-up as a reseller on the seller's web site and they give you a link to track your prospects and sales. Every time someone orders through your link you receive a commission.