The number of young people seeking help because of problems with housing letting agents has more than doubled over the past two years, a new report reveals.
Citizens Advice said university students moving into privately rented accommodation this month were likely to be among those "stung" by having to pay hundreds of pounds for poor service.
The charity dealt with 6,500 cases in the year to June, including over 800 from 17 to 24-year-olds, with research showing complaints about delays getting basic repairs completed, or with high fees.
The price of letting agents' fees have risen by up to 60% over the last five years, with the average increasing from £125 in 2009-10 to £200 in 2014-15, rising to £700 in some cases, said the report.
Letting agents charge fees for admin tasks such as preparing the tenancy agreement, checking references and credit checks.
They may also require the tenant to pay a holding deposit after a prospective tenant has agreed to the rent but not yet signed the tenancy agreement. These fees are often non-refundable, and are charged on top of advertised rent prices and deposits for the property.
The charity is calling for a ban on letting agents charging tenants fees.
Gillian Guy, chief executive of Citizens Advice, said: "Letting agents are hiking up their fees for a service that's often not up to scratch.
"With fees rising year on year for letting agents, many tenants will rightly be wondering why they are paying hundreds of pounds for a simple contract renewal or for management services that leave them waiting months for essential repairs.
"It is concerning that younger renters are among the most likely to report problems with a letting agent, when many will end up using letting agents to find somewhere to live at university.
"Private renters shop around for properties, not for letting agents. Landlords are better able to choose agencies based on performance and cost and it should therefore be landlords paying letting agent fees, not tenants picking up these rising costs."