Around 23% of people surveyed by the housing charity Shelter believed they had been landed with unfairly high fees for aspects of renting such as credit checks, renewing contracts and "administration".
Shelter said it had found cases of renters being charged more than £150 for repeat credit checks every year, which the charity said actually cost between £8 and £25 to perform.
It said some people were being charged £100 just to view a property and renters were being charged up to £540 in non-refundable "administration" fees.
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The property developer painted the mews house in March last year after she was denied permission for a basement below the property.
Profits at the estate agent plummeted 42% in the first half of the year.
Ionut Gheorghe, 27, was detained in Los Molinos near Madrid on Friday by Spanish police under a European Arrest Warrant.