The warning follows the latest Complete University Guide figures, released this week, that show a large drop in graduate starting salaries.
Starting pay, if inflation is taken into account, fell 11% between 2007 and 2012. This is more than double the 4% decrease recorded between 2005 and 2010. In 2012, the average graduate starting salary was £21,702.
Only two areas showed an increase in starting salaries over the period: technology materials (up 13%) and librarianship and information management (up 3%). The sharpest decrease in starting salary came in medicine, with a fall of 15%.
Isherwood said he expects starting salaries to begin rising again and people should take into account more than just initial financial reward when considering a job.
"Graduates must ensure that they are concentrating their efforts and applications towards roles that best suit them, their aspirations and their skill set," he said. "Potential earnings should be part of that consideration process."
Isherwood added that many of AGR's clients had positions available, even in the worst days of the recession.
"It’s worth noting too that many of our members reported unfilled vacancies, so we should avoid generalising and painting too bleak a picture for current students and graduates," he said. "A good university degree will still stand you in good stead and there are opportunities out there."