Martin Lewis gained fame thanks to savvy tips and campaigns that saw bank charges and PPI payments handed back to customers who had been badly treated.
But it was a completely different piece of advice that saw one of his readers get an incredible £11,500 returned to her.
How did she do it? She checked her tax code.
"I'd never done it before, but you gave me the confidence," Tina told MoneySavingExpert.com in an email last week.
"After I was recently made redundant, I got my P45 and phoned HMRC. I said: 'Look, can you just check this for me?'
"They checked a couple of things and asked: 'Can you stay on the line?', before saying: 'We owe you £11,486 - how would you like it paid?'
"The cheque arrived 10 days later."
And it applies to everyone.
Martin, writing in the MoneySavingExpert.com weekly newsletter , said: "It's not just for those who are made redundant. Everyone should check their tax code - millions could be wrong."
Mirror Money has seen cases where people have got thousands back after mistakes were made when they were promoted or changed jobs, while thousands of workers in Wales were recently warned they may have overpaid on tax too.
But it's all too easy to miss this.
"I had just trusted the amount of money HMRC had taken off my redundancy pay - my instinct kicked in after your warnings," Tina wrote.
"This success has allowed us to clear our debts and plan for the future. I am so grateful. I just want one person who reads this to pick up the phone to HMRC and have the belief to do it."
What to look out for yourself
Everyone with a boss or a pension has a tax code. It's how HMRC works out how much of your income you pay tax on.
It takes the form of a letter and a few numbers on your pay slip, and mistakes could cost you thousands of pounds a year.
They change based on your age, where you live, how many jobs you have and even if you're married sometimes.
We have a full guide to .
"Errors are common though, so don't assume you're on the right code. Many are wrong, meaning you can be over or underpaying tax," Martin wrote.
"If you have paid too little, you may have a horrid bill coming. If you've overpaid, you could be due cash back. Full help in our Tax Code Calculator guide."
If all that sounds like too much work, MoneySavingExpert.com has a free Tax Code Calculator that can help you work out if yours is wrong.
"If your tax code doesn't look right, it probably isn't," Martin wrote.
You can check online if you may be entitled to some money back, and make a claim through the government’s website .
While the process can take around 12 weeks, things don’t always go smoothly so you may be waiting a while for the money.
If you want to raise a complaint to HMRC in a bid to hurry things along, then it’s worth trying free complaints site Resolver which can help with the process.
