While having some basic understanding of marketing is useful, as Chardo said, the key requisite is selling skills. Selling is a talent, if you have it, it can (and will) lead to a very long and successful career.
Using UF’s Sale Engineering minor (16 to 18 credits) as an example of the type of courses that could be useful to a sales engineer.
Keep in mind a sales engineer doesn’t need to minor in it, but this gives one a good idea of what UF thinks would be useful for someone entering the field.