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.
They are all related but in different categories.
This is how they are related:
- Industry
- Organisation
- Company; Profit Organisation ("Business")
- Corporation ("Co.")
- Public Limited ("Ltd")
- Private Limited ("Pte Ltd")
- Incorporated ("Inc.")
- Trust company
- Agency
- Firm
- Partnership
- Limited Liability Company ("LLC")
- Limited Liability Partnership ("LLP")
- Non-profit
Disclaimer: The chart above is incomplete as it is just to let the OP to have the image of how they are related.
Disclaimer 2: I am unsure whether Industry includes Non-profit. I don't think so, I think it includes categories of businesses like Automobile, Telephone, Internet, etc.
The most common mistake people make is the usage of Company, Corporation and Firm.
Best Answer
I cannot speak to English elsewhere, but in the US there would be no need to use size at all—‘small business’ is the term.
If you are concerned that bare small suggests inferiority, quite the opposite is true. ‘Small businesses’ are generally recognized—or at least recognize themselves!—as the engine which drives the American economy, and there is a large Federal agency, the Small Business Administration, dedicated to their support. They have indeed something of a mystique: ‘small business owners’ regard themselves as a distinct class, superior in efficiency, energy and entrepreneurship to the bureaucratic managers of large corporations.
Of course the US notion of ‘small business’ may be substantially larger than that which obtains in your country. The SBA standard varies from industry to industry, but by and large it is less than 500 employees in manufacturing and less than $7M annual revenue in non-manufacturing industries.