I am a long-time client of North American Bancard's payment processing services and have referred dozens of business owners to NAB for their own credit card processing services as well over the years. The rates are fair and the setup is quite easy.
An area that any large business occasionally has problems with is their call center and the queues you sometimes have to sit through to reach a representative when you need to speak with someone. NAB has taken steps to speed the process along, but there are times when you may be sitting on hold for a few minutes before being able to speak with a representative.
Make sure you know what your terms are and that you are working with a reputable sales person.
I needed to be able to accept credit cards as a form of payment from my customers. NAB has helped me be able to do that.