I read a lot about the difference between customer and client. There have been a myriad of answers, and the most common thing I could find is the one that matches Hellion's answer here:
Client – ongoing relationship with the seller.
If you go to the store to buy a box of matches, you're just a customer, but if you always go to that store because you know you'll get good service and good prices, you're a client.
Now the question
I have heard many people say:
Take care of him, he's our regular customer
But…
Can a customer be loyal or regular?
If they can be, they are no more customers but clients!
Furthermore, is this sentence correct (or redundant)?
He's our regular client!
Best Answer
Client and customer are no longer distinguished in the way they once were.
As recently as fifty years ago, client was still by and large reserved for people who sought advice from ‘professionals’ such as attorneys and architects. At that time client still reflected, even if only very dimly, the original Latin sense of the word as “one who is under the protection of” a patron. A client was someone who benefited from the professional’s learning and knowledge, while a customer was someone who had a purely commercial relationship with a tradesperson.
In this context, the term client acquired an honorific character. It flattered the person rendering services because it imputed a ‘professional’ degree of expertise; it also flattered the person who purchased the services because it imputed a degree of wealth and status—a person who routinely consults professionals is clearly someone above the common run of customers. And it happily set both at some distance from the vulgarity of commerce.
In consequence, from the last half of the 19th century, businesses of all sorts started referring to their customers as clients—‘exclusive’ tailors and hairdressers, grocers, insurance agents, even bookmakers (now calling themselves ‘turf accountants’). And since it is mostly businesspeople who talk about the relationship between buyer and seller, that use has gradually extended into ordinary speech.
The upshot is that today there is no difference whatever between customers and clients—they are the same people. Instead, customer is used when you wish to focus on the financial aspect of the relationship, client when you wish to focus on the personal service rendered.