Sales tactics and activities are generally focused around pushing or reaching out to people to get them to engage, whereas marketing tactics and activities are generally focused around pulling in, or attracting, people to engage.
Sales becomes marketing when quality, value adding relationships are formed – think of when a customer comes to you seeking advice and direction.
Marketing becomes sales when the focus is on quantity of connections, over quality – think of email marketing, where the content is generic and the hope is that once in a while one connects with the recipient.
They are independent, yet interdependent. Separate, yet reliant on each other. When they find the perfect balance and work together they are a powerful force.