Scam calls don't succeed because people are foolish. They succeed because the callers are practised at a handful of techniques that work on almost everyone. Once you can name the technique being used on you, it loses most of its power. These are the ones that come up again and again in reports from people who were called.
Borrowed authority
The caller claims to be from somewhere you're inclined to obey: your bank's fraud team, HMRC, the police, the council. They use titles, case numbers and confident, official-sounding language. Many people find it hard to challenge a "police officer" or put the phone down on "the bank".
Break it: remind yourself that real authorities don't mind you checking. Say you'll call back, then hang up and ring the organisation on a number you've found yourself.
Manufactured urgency
"Your account will be emptied in the next hour." "Officers are on their way." "This offer ends today." A deadline stops you from talking to anyone else, from sleeping on it, or from checking.
Break it: treat urgency as the warning sign. Genuine problems still exist in ten minutes' time, after you've checked.
Fear
Threats of arrest, court action, deportation, a frozen account or a hacked computer push you into survival mode, where you'll do what's needed to make the problem go away.
Break it: notice the fear and take it as a signal to stop. A call that makes you panic is far more likely to be a scam than a real emergency.
Already knowing things about you
The caller has your name, address, bank, or the last few digits of your card. That makes them seem legitimate. In reality this information is often bought after data breaches, or taken from social media.
Break it: knowing your details proves nothing. Never "confirm" anything to a caller, even details they already seem to have.
Isolation
"Don't tell anyone at the branch, they may be involved." "Don't hang up or the case will be closed." Scammers try to keep you on the line and away from anyone who might talk sense into you.
Break it: any instruction to keep a call secret, especially from your own bank or family, is a red flag. Talk to someone you trust before you act.
Small steps
The first request is tiny: confirm your postcode, read out a code "to verify you", download a harmless-looking app. Each step makes the next one feel normal, until you're moving thousands of pounds.
Break it: decide in advance that certain things never happen on a call, however small: reading out codes, installing software, moving money.
Kindness and rapport
Not every scammer is aggressive. Some are warm, patient and apologetic, especially in romance, investment and "refund" scams. They may call several times over days or weeks before asking for anything.
Break it: friendliness doesn't make a request genuine. Judge what's being asked, not how nicely it's asked.
A script to keep by the phone
If you're ever unsure, these few words work for almost any call: "I don't deal with this over the phone. I'll contact you myself." Then hang up. If it was genuine, nothing is lost. If it wasn't, you've just ended a scam.
Afterwards, look the number up on Who Called Me Check and add a report describing the script. It helps the next person recognise it faster.
Not sure about a call you had?
Look the number up to see what kind of line it is, where it's from and what other people said about it.