What are your biggest barriers when using a recruitment consultancy? (Candidates AND Hiring Managers)

I have recently moved from a resourcing position within 1stExecutive, onto a full 360 Consultant role within Energi Professional I have been tasked with the fantastic challenge of building an Interim Procurement Recruitment Specialist Practice. One of the interesting things I've noticed, is the reputation of recruiters in the industry. I have developed trusting, open and collaborative relationships with the majority of my candidate network, and am very keen to do the same with my clients. One of the things that truly helped me stand out to my candidates, was finding where they'd been let down by other agencies, and making a commitment to them in regards to this area. So - What are your biggest bug-bears, barriers or pet-hates with using recruitment agents?