That is one of the headline findings in a poll conducted by Marketing Week, which also revealed that just over half (52%) of marketers are fairly happy with the service they receive from agencies.
More than two-thirds (67%) of brand marketers regard trust as the most important attribute they look for in their agency partners, yet just 15% believe agencies fully deliver on trust, based on a score of five out of five.
More positively, when taken together with the 46% of marketers who score agencies four out of five on trust, it means the majority still trust their agencies.
However, the survey found just 29% are positive that agencies deliver cost efficiency, which is an attribute ranked by 52% of respondents as being key.
Furthermore, agencies get a score of just one or two out of five from a quarter (26%) of marketers, signalling dissatisfaction with the results of what they're paying for.
The survey findings appear to reflect general unease among some brands about continuing to work with agencies along traditional lines.
Some brands have moved much of their ad creation work in-house, including sandwich chain Pret A Manger and mobile network Three, while others have dispensed with creative agencies when designing their campaigns.
Lenovo, the Chinese tech giant, for example, used a crowdsourcing platform to develop ideas for a video and TV campaign to promote its Yoga products.
Meanwhile, some major agencies are responding by adopting new network models to meet their clients' changing needs.
Omnicom Group has launched a collaborative network called Shape, which was piloted by C Space, one of its agencies, to enable clients to access the collective talent of the network across the world.
With a global network to hand, the aim is to provide clients with a wider pool of talent and for work to be turned around more quickly, and Felix Koch, managing director at C Space, said he believes other agencies will start to try out a network approach.
"There is a trend towards relying less on traditional agency structures and thinking about how you can create experts to work on briefs," he said.
Data sourced from Marketing Week; additional content by Warc staff