I overheard a cab driver being scammed by someone claiming to be HMRC (UK version of the IRS), and when he asked to call them back they managed to convince him to call them back on Viber, and he was about to when I intervened and pointed out to him that 1) what I'd overheard was blatantly a scam, 2) if he was unsure, to go to their official website and find their number...

If you're going to get people to call you back, it has the problem of ensuring that they call you back on your real number - giving reasons why they have to call you back on some other number is way too easy ("I've lost my phone", "my phone is at home", and so on)

Also, make sure to use official website, not just Google search, or any chat agent question, the SEO are sometimes poisoned with scam phone numbers.

I consider myself always to be wary of scams and my trust-level is zero when they call me, but I recently almost got myself hooked on an airline support call. I google searched the support number and trusted the AI summary on top and called it, they asked me my reservation number and I happily provided. With the reservation number they have public access to the entire reservation details, they knew my name, my flight, my co-passenger details everything. I called to do a reservation for my pet which is normally not done online. their problem, they got greedy and asked me more than pet travel, iirc they said there was a problem with one of my flights, it wasn't paid and I had to repay on the call. If they just followed along instead of going by the script I would have paid the pet travel amount.