Politicians - really, anyone need an explanation. It's part of the job to deceive.
Journalists - joke profession now. Can't even trust the BBC. Some of the rubbish they've fed us is revolting.
Policemen - bloody useless. Attracts laddish types.
Insurance claim handlers - they have quotas to meet. Disgusting.
Loan Companies / Sales people (anyone who works in them) - tell you anything except the small print to make a sale.
Bankers - disgusting.
Lawyers - studied and worked in law so know better.
Customer Service Agents (in most businesses) - poorly trained with no desire to learn or work, appaulling attitude, will lie to get you off the phone. Trust what they say at your own peril.
I have an inherent distrust of self-employed technically skilled people. That's due to my own lack of knowledge though, I don't trust them because I can't challenge what they're telling me. I always get 3rd, 4th even 5th opinions.
Also have a growing distrust of people who served in the army. Possibly due to a couple of friends who've returned from service and have became, odd to put it lightly. Can't trust them to pay back 10 quid, or to keep their mouth shut with some info they shouldn't be talking about, like they don't give a toss anymore and they'll do what they want.