Although letting agents are largely unregulated in law, they still have a certain amount of legal commitment to inform, manage and fulfil a duty of care to their client landlords.
Some agents fail on all counts or attempt to 'pass-on' the responsibility of dealing with a contentious issue, simply because it is easier to do so.
The wise approach would be to scrutinise the proficiency, accountability, services offered, experience and professional organisation membership status of letting agents in your local area before deciding which to employ.
However, perception after the fact is a lesson often learned by those stuck with a rogue or under-performing letting agent and isn't of much use when things suddenly go pear shaped.
Regardless of the problem, there are a number of procedures useful in dealing with complaints against letting agents - and the success of each relies on the internal policies of the agent together with the wording of the signed contractual agreement and the bearing of common and statute law.