The UK's official consumer advice body Consumer Direct dealt with a record 819,815 complaints in 2007, marking an 18% increase on the previous year.
Second hand car sales by independent retailers prompted the highest level of complaints for the second year running, rising by almost a fifth on 2006.
Complaints about mobile phones were also considerable, while issues with phone handsets also spurred complaints.
More than half of users who resolved their complaint saved more than £100.
As well as the 41,800 complaints about used second hand car sales from independent retailers, there were a further 13,322 complaints about second hand cars bought from franchise dealers.
Consumer Direct operations manager Michele Shambrook said the increased level of complaints means consumers are more prepared to tackle poor customer service.
"The rise in complaints in 2007 reflects, in part, a growing awareness of the service among the general public, as well as an increasing willingness among consumers to complain when they buy unsatisfactory goods or receive poor service," she said.
"Consumers are finding that by arming themselves with information about their rights, they stand a better chance of resolving problems with shops and traders," she added.
According to Consumer Direct, more than half of those who used its service to resolve their complaints, were compensated through a combination of refunds, repairs and replacements to save more than £100 each.
And nine percent of those surveyed had saved more than £1,000.
Consumer Direct, which is government funded, offers advice via its website and through 350 staff based in 11 call centres across England, Wales and Scotland.