Before letting a property to tenants, private landlords and agencies have to meet the UK legislative requirements.
The property must be safe for tenants, including gas, electrical and fire safety.
The property must be clean with prepared inventories and documents for tenants.
The landlord or agency knows the whole letting process, including finding and identifying target tenants, referencing and the tenancy agreement.
The deposit must be managed properly and registered.
If you are an estate or letting agent, you must join a Redress Scheme.
More details on this Government 'How to Let' guide, https://www.gov.uk/government/publications/how-to-let/how-to-let