Over-politeness is blamed for costing the average UK household nearly 3,000 a year in missed refunds, discounted goods and poor service.
Nine out of ten people surveyed always pay what they are asked without question, even if they are unhappy with the deal.
One in three does not bother to get refunds on goods they find they do not want, or need, according to the poll of 2,500 consumers carried out for consumer website moneysupermarket.com.
Two out of three people will not complain when they receive bad service in a hotel or restaurant, and will even pay a tip.
Psychologists claim that busy consumers, overloaded with chores, errands and shopping lists, may simply lose track of returning or complaining in time.
The survey showed nearly 60 per cent of people said they did not have time to complain or return goods.
Psychologist Dr Tracy Alloway, director of the Centre for Memory and Learning in the Lifespan, said an unwillingness to complain was deeply rooted in British society.
"It's a lot different from America where the customer is right. Here it's that you don't want to bother someone, so if your coffee is cold, you wouldn't want to ask them for a new cup," she said.
But attitudes are changing rapidly, she suggested, with the impact of globalisation and increased travel to other countries where hard bargaining and speaking up is the norm. Britons may be more ready to demand their money back than they were five years ago, she said.
Clare Francis, of moneysupermarket.com, said: "Our Britishness appears to hold us back from being more demanding and making the most of our money.
"It's understandable that people don't want to look foolish, appear rude or make a scene, but our reserve is potentially costing us each hundreds if not thousands of pounds every year."
Research has found nearly two-thirds of shop owners and managers say recession means they would offer discounts to close a deal if asked. Consumers are said to feel most comfortable negotiating on electronic items such as TVs, DVD recorders and stereos.
But a third of shoppers have never tried to negotiate a price down on something they are buying. Only 10 per cent said they haggle on a regular basis.
With the average discount reckoned to be 13.5 per cent on two-thirds of UK household expenditure, the cost of lost discounts and returns from over-politeness was calculated at 74bn.
Dr Tracy Alloway: There's no stigma – you're the one who earned the money