I have to second Agent.
I have lived in Weymouth, a coastal holiday town with a completely messed up economy. I had two years of university education under my belt, so I wasn't at all uneducated.
All the well-paying jobs were either extremely limited in number (you can't have 50 supervisors per fast food outlet, can you?), seasonal (usually also highly limited in number), required specific training (nursing, teaching) or required a driving licence.
Almost all the low paying jobs simply would not hire someone of my training (seriously, education can be a total put-off at times).
What other jobs occasionally cropped up (but failed to do so whilst I was there) were agency work. As someone I believe has commented, agency workers don't figure properly into government figures. They are also a total ripoff for the employee, and would be for the employer if it were not for the vast flexibility and fluidity they allow.
And yes, exactly as Agent said, there are also the regular people who for various reasons simply do not have the ability to earn any more, no matter what incentives you offer or training you provide. Perhaps in an inner city area up north that is not a major issue, but...
The big problem in Weymouth was simply the cost of living. It was on the south coast, with a highly seasonally varying economy. In general, rent was extremely high for what you got, and very limited availability of alternative accommodation existed (often meaning, for example, pre-pay meters). We actually officially lived below the 'poverty line' (where more than half your income goes on rent and power). This was despite my partner having a reasonably (for the town) well paid job. For most people, earning enough to be able to gain access to means to earn more was nearly impossible.