Does a Devon business need a website if they're already getting work through word of mouth?

Yes. Word of mouth has a ceiling, and even referrals Google you before they call. If they find nothing, or something that looks amateur, you lose the job before you've spoken to them.

• Facebook is not a substitute. Meta controls your visibility, not you
• Algorithm changes can wipe out your reach overnight
• You cannot rank on Google from a Facebook page alone

Your website is the only online asset you own and control completely. It works for you around the clock without you lifting a finger.