If you have a customer's number because you completed a job, that does not automatically mean you can send them every future offer. A message containing a new promotion is different from a reply they asked you to send about a quote or appointment.
The Information Commissioner's Office (ICO) explains that the Privacy and Electronic Communications Regulations (PECR) restrict electronic-mail marketing to individual subscribers. Email and text are common examples. Messaging apps can have their own terms and may fall within electronic-mail rules depending on how they work, so do not treat WhatsApp as a loophole.
Separate service messages from promotions
If a customer asks for a quote, send the quote and necessary follow-up about that request. Keep it focused on the work they enquired about. Adding an unrelated seasonal offer, referral request or campaign can turn a service conversation into direct marketing.
Before sending a promotional message, record which rule you are relying on. For individual subscribers, the ICO says you generally need consent unless the limited “soft opt-in” applies. That exception is not a general permission to message any former customer: it has conditions around how you obtained their details, offering your own similar services, and giving an opportunity to refuse marketing.
Sole traders and some partnerships are treated differently from limited companies under PECR. Do not assume that a business email address means the subscriber is a company; the ICO's guidance explains how to identify subscriber types. Data protection rules can still apply when a message identifies a person.
Make opting out straightforward
Identify your business, explain why the person is receiving the message, and give a simple way to stop future marketing. Keep a suppression list so that an opt-out is respected if you later change email or messaging tools.
For WhatsApp or another messaging service, check both the ICO's current direct-marketing guidance and the platform's business messaging policy. Do not add customers to a broadcast list just because they contacted you once.
A pre-send checklist
- Is this a reply the customer requested, or a promotion?
- Is the recipient an individual or a corporate subscriber under ICO guidance?
- Do you have valid consent, or does a specific exception apply?
- Can the recipient identify you and opt out easily?
- Have you recorded the source, purpose and preference?
Read the ICO's guidance on electronic-mail marketing and the soft opt-in. This is general information, not legal advice.