If you're talking about syncing their customers' phone numbers from their customer's Mac to their customer's phone, then they can have the customer do that with their own credentials.
If you're talking about the business person syncing their own collection of contacts (customers and otherwise) between their own devices, that should also not be a problem.
Unless there is a specific privacy law for a specific country that forbids it, if the company providing the syncing service (i.e. Apple) has a privacy policy in place (which they do) that prevents use of that synced data by the service provider, there shouldn't be any privacy concerns.
If you review it on their website, you'll see Apple has an EXTREMELY unforgiving privacy policy that prevents them from doing anything with that data besides storing it for YOU, and syncing it between YOUR devices.
In fact, they can't do anything to your iCloud account if there is an issue without first verifying your identity and obtaining your express consent.
Fact checking is always helpful.