Canny consumers who are coming to the end of year-long fixed rate gas and electricity fixed rate deals are in for a shock.
When you look at the price comparison sites to see what you'll be paying next, it's likely to be £100s more.
But that won't be the only surprise.
The switching services will promise you huge savings, like this:
How is there a saving of nearly £400?
Well, it's compared with what you would be paying if you didn't switch deals and you ended up on your current supplier's Standard Rate (the expensive one).
In fact, in this example your best option would be a near £200 increase in your annual bill.
Of course, if (like most people) you're on the Standard Rate already or have never switched before you are likely to make a substantial saving anyway.
For the rest, make sure you click "What will I pay?" and avoid disappointment...