A marketing writer is one who is able to write all your sales and marketing materials in order for them to appear professional and get you more customers.
If you are looking for work that is high-end and able to reach out to your niche audience then a marketing writer can certainly do that. They have an uncanny knowledge about the market and the pulse of your customers, the customers who are going to buy from you and leverage you, in the top league. This is because of the number of sales that the marketing writer is able to garner by reaching out to people who matter with their writing.