Cynicism is a variety of compliance in advance. It creates the conditions it decries.
Obviously there are corrupt politicians. But also obviously there are politicians who actually want to advance the public interest. It is the job of voters to tell them apart and ensure only the latter become the custodians of state power.
There have certainly been a few exceptions, but they're few and far between - and tend to be because of special circumstance. For instance I think Bernie Sanders, before he tried to run for President, was a good guy. But that's because he's from Vermont, a state with a smaller population than El Paso, TX. Democracy works quite well with small populations, but not so well with with larger populations when the 'distance', speaking both metaphorically and literally, between voters and their representatives grows too far. It also tends to fail when societies become too divided.
As for the voter determining who's socially motivated and who's a silver tongued conman? I don't think that's at all realistic.