Hello.
1. There should be an option for vendors to buy advertisement for a product(s) for a fixed amount of price and time.
The products would be "featured" at the top of category they are in, and will rank higher when user searches for "tags" and "keywords".
Dokan has this option.
2. Use Stripe as middle-man, consumer buys the product and money is automatically split between admin and vendor.
Dokan has this option.