What's one way to deal with a high-maintenance customer?
Some customers require much more effort on your part. They are "high maintenance" kind of people. They take forever when they come to talk with you, need to be repeatedly contacted to move the order along, are rude to you or your staff, are very slow to pay, or it's just something that makes you go "ugh" when you hear from them.
For these customers, consider adding an HFF (hassle factor fee) to their orders. It's subjective with a sliding scale from 10–25%. Depending on how difficult the customer is, increase their prices per piece. Once the HFF is added to their pricing, the "ugh factor" usually goes away because you get paid in proportion to the level of maintenance a customer requires.
If you want to make profits, you need to find ways to encourage your problem customers to either pay you on time or the amount you set so the next time you hear from that customer, your gut does not get twisted up with, "Oh no, here we go again." It will be much more satisfying when you hear from them as you know that you will be fairly compensated for your services.