I personally don’t believe that ALL politicians lie. Many of them lie, many politicians also avoid speaking about unpopular things (and the blame for that lies also to the citizens) and there are some of them that also (try to) tell the truth.
I don’t believe that the majority of citizens are stupid. The most important thing for a citizen is to be interested enough about politics and not to be dogmatic. After that, i really believe that almost any citizen could listen carefully to the arguments of each politician and understand if, for example, Sanders’ points against Trump are true or he just says them for harming his political opponent.