shitweazel

1)A shady or duplicitous person. A confidence trickster or scammer. A member of a group liable to defraud others - for instance, solicitor, estate agent, bank manager etc.
2)Someone who seems to thrive in an unpleasant environment and always seems to be at the heart of any problems being created.
3)Some it is difficult to prove guilty of fraudulent, unsavoury or similar acts.
Imagine a pile of excrement, with a slippery weazel popping up, looking left and right while standing up with the excrement on this head, like a proud hat, and then disappearing down again.

"I had a call from Natwest again. They are trying to sell me PPI but its clear I'll never be able to make a claim. They never get done for fraud. They are such shitweazels".