Used cars bought from independent dealers drew the highest number of complaints from disgruntled consumers in the last year, according to new figures.
Citizens Advice has called on retailers to display consumer rights information at checkouts after more than half a million people complained about shoddy products worth £3.5 billion in the last year.
Figures show 45,000 used car buyers lodged a complaint in the year to February, followed by 12,000 regarding mobile phone contracts and 11,500 about repairs by an independent garage.
Other top grievances were about upholstered furniture, mobile phone handsets and laptops, notebooks and tablet PCs, followed by women's clothing, general building work, televisions and beds and mattresses.
Citizens Advice Bureaux dealt with a further 370,000 consumer problems in 2012, with 1.6 million people seeking advice online and five times as many people visiting its website this February compared to last February.
In a separate study, consumer group Which? said UK shoppers lost out on an estimated £1.2 billion over the last year by not exercising their right to return goods.
Which? executive director Richard Lloyd said: "With household budgets severely stretched, it's staggering to think that collectively people have lost out on more than a billion pounds by not returning goods when they had the right to.
"The Government must not delay its plans to make consumer law simpler, clearer and stronger to empower consumers and boost standards of service. That will be good for growing businesses that treat people well, good for competition and good for the economy.
"Our new consumer rights website is really easy to use and helps people know what they're entitled to, with practical advice on how to get your money back."