Customers hear you say, "here, I made this," and they buy or they don't buy.
Clients say to you, "I need this," and if you want to get paid, you make it.
The customer, ironically, doesn't get something custom. The key distinction is who goes first, who gets to decide when it's done.
The provider is rarely better than the clients he is able to attract. On the other hand, the creator often gets the customers she deserves.