Competition lovers claim they are being "taken for a ride" by prize draws which do not give out all the prizes advertised.
A number of "compers" say a contest being run by frozen food brand McCain is one example - the headline prize fund looks impressive, but the chance of winning is slim because not all prizes are guaranteed.
As the Advertising Standards Authority (ASA) considers whether to investigate McCain's promotion, BBC News looks at three current promotions - two of which have also attracted complaints.
The watchdog is encouraging people to come forward if they think a prize draw turns out to be less generous than it seems.
"It's important promotions deal with participants fairly and honourably," an ASA spokeswoman said. "We only need one complaint to investigate - so we would encourage anyone with concerns to get in touch."
McCain is advertising a £3m prize fund in its Great Village Raffle, with what it says is the chance of winning one of 26,000 prizes, including cars, spa retreats and restaurant meals.
But while all the prizes are "available to be won", a large proportion almost certainly won't be.
Entrants must submit a code from the inside of a product packet, along with their email address, to the promotion's website and prizes are then "randomly assigned" using an algorithm verified by an independent third party.
Unlike a traditional village hall raffle, you don't stand more chance of winning if fewer people enter.
Blogger Di Coke, who has been entering competitions for 20 years, said customers were being "taken for a bit of a ride".
The promotion is also being looked at by the ASA, which has received one complaint.
"People think, '£3m of prizes. There's almost 30,000 prizes advertised in this competition. I've got a good chance of winning,' and people really haven't.
"The only way all £3m of prizes will be given away is if every single code on every single promotional packet is entered on the website."
Realistically, she explains, that won't happen for a variety of reasons - people don't realise their pack contains a promotion, they forget to enter, can't be bothered, lose their receipt, can't find or read the code - or because the products are still sitting on supermarket shelves after the closing date.
'Not this time'
Di, from Brighton, says these sorts of promotions are becoming more common.
She says it's likely only about 5% of the available prizes will ever be given out - a figure backed up by Jeremy Stern, from PromoVeritas, a company which runs competitions on behalf of big firms.
But he points out: "If more people would enter, more people would win."
Francesca Jones, who has been trying to win in the McCain promotion, told BBC Radio 4's You and Yours: "Every code you put is, 'Sorry you're not a winner this time.'
"I have got a lot of friends who are trying the competition in the group I'm in and not a single person has won which is really unusual. Comping is our thing."
The terms and conditions in McCain's promotion make clear there is "no guarantee that all prizes will be won".
A McCain spokesman said: "We can confirm that customers are winning prizes in the McCain Great Village Raffle promotion and there are still many more exciting prizes to be won until the closing date of 31 January 2018."
Jarlsberg's shopping spree
Jarlsberg Cheese is running a competition offering up to £50,000 worth of shopping vouchers that can be used at more than 120 High Street stores.
The ASA said it was assessing four complaints made by consumers.
Entrants need to buy a promotional pack of Jarlsberg slices or a wedge and enter the product's barcode into a webpage to find out if they have won.
In order to claim the prize, entrants must keep the original itemised till receipt as well as the winning pack.
Some 1,032 vouchers are available to be won - from £20 to £1,000 - but according to the terms and conditions, all of them "are not guaranteed to be given away".
'Bit of fun'
Stuart Clarke, of Fearless advertising, which represents Norseland, the parent company of Jarlsberg Cheese, said: "When you have a promotion the view is that it is value added on top of the purchase of the product.
"We like to make the prize fund as attractive as possible."
He said to have a guaranteed number of prizes would be more expensive than a "chance to win" and would result in dull prizes that are not as attractive to the customer.
"It is a bit of fun," he said. "The terms and conditions are always really transparent."
Onken's blender blitz
Meanwhile, Onken yoghurt is running a promotion where customers could win one of 50,000 NutriBullet blenders. It has not attracted any complaints to the ASA.
Entrants can only be accepted online, and will need to enter the promotional barcode found on the lid of the pack.
Winners, who are chosen randomly by an algorithm, will also need to keep their packs and the original till receipt as proof of purchase.
Again, the terms and conditions state: "Although all prizes will be available to be won, there is no guarantee that all prizes will actually be won."
And they add: "The number of prizes won will be (statistically) dependent on participation rates."
A spokeswoman from Emmi UK, the parent company of Onken, said the promotion was "legally compliant and fully complies with the Institute of Promotional Marketing's guidelines".