We do marketing partnerships with some of our ongoing accounts. Terms vary from fixed-fee retainers through fixed amount + 10-20% split share to 30-40% fee on new deals.
Depending on the specifics of the business and the marketing services provided, the percentage could be for a specific product/service, or the entire business. We do inbound marketing and partnership outreach which increases the brand awareness, grows the email lists of our clients and allows for scheduling cross-promotion campaigns and webinars that support the entire business - hence the added benefit of shared revenue across all products and services.
Limiting revenue share for a product is more applicable for larger businesses that have an established marketing and advertising strategy and bring a good number of customers this way. Then a marketing strategy could be shaped around a specific product or a solution which justifies partnering only on a specific venture.