Credit brokers have been accused of being "menaces" and causing harm to consumers by a leading consumer rights organisation.
Citizens Advice has warned that credit brokers often charge higher fees than originally agreed and bill customers for services they didn't even ask for.
Two in five people who complained about a credit broker to the organisation over the summer had problems with up-front fees. Among them, 58% were charged unexpected fees of as much as £70.
A fifth had their card details passed on to other brokers without their knowledge and 19% had not applied for a loan. Other complaints included having their cards charged even though they had not even completed loan applications.
Citizens Advice said the firms are also cashing in on the demand for short-term credit and in some cases have pretended to be payday lenders.
"Often consumers believe they are dealing directly with a payday loan company because websites or marketing text messages from some brokers do not make it clear they are a broker," it explained.
"Borrowers are then hit with an unexpected fee and in some cases don't actually go on to get a loan."
It gave the example a young woman who asked Citizens Advice for help after applying for a payday loan and within seconds being inundated with texts from other payday lenders.
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"She contacted two or three of them but decided not to take out a loan. Over the next few days she found that several sums had been taken from her bank account by different brokers, despite the fact that no loan had been given," Citizens Advice said.
Analysis from the consumer group also found that while broker fees are refundable if a loan isn't taken out, "borrowers are finding themselves up against a brick wall when they try to get their money back".
Looking into 228 cases where consumers had tried to get a refund, it found 28% were refused, 14% were promised a refund but never got it and 42% struggled to get in touch with their broker to deal with the matter.
The Financial Conduct Authority will regulate the consumer credit industry, which includes payday lenders from April, and Citizens Advice wants it to "take an equally tough stance against credit brokers".
Its chief executive Gillian Guy said: "Credit brokers must be transparent about the service they offer and any fees they charge. The FCA needs to recognise the harm menaces in this industry can cause and come down hard on those who break the rules.
"Preventing unscrupulous brokers from entering the market in the first place, through a strict authorisation process is essential. The FCA should also be seriously concerned about the prevalence of data sharing among brokers as money is being siphoned from people's bank account without clear permission."