It's great to have a really big customer so you don't have to deal with lots of little customers. Well, it's great to have a big customer until it's not. Our rule is that no one single customer should ever represent more than 20% of your revenue. If they do, they have a lot of influence and control over your business. This can be a scary situation. Many small businesses have been put out of business simply because a large customer decided to go with a competitor's offering. But before you go ridding yourself of your top customers, there are many strategies you can employ to guard yourself when dealing with that one big customer.