Anyone who is in a purely sales function has to worry about collections to a degree, but for the most part he or she can always be the good guy. When collecting sales that were made on account becomes an issue, the good guy salesperson can always refer to the "collections department."
There are those of us on this site who have not only a sales role, but also that of small business owner or consultant. We can sometimes be torn between managing the relationship as a good guy, but have to wear a "bad guy" hat when it comes to collections.
I generally stay with the "Good Guy" hat as long as possible. If a customer owes a decent amount of money, I often ask what I can do to help them... a payment plan, or something along those lines. During the course of this strategy, I then ask the customer to make at least some payment before we provide any more product or service.
What approach do other people on the board take?