If you were to draw a Venn Diagram of the skill sets of salespeople and politicians, it wouldn't quite be a circle, but I suspect it'd be pretty close. Politicians exist to convince you that they are going to represent your interests in whatever level of government they are running for. Once there, they need to negotiate for their policy positions with the other elected representatives. The main difference is that the currency of politicians is votes, instead of money.
Sure, some of them might actually believe the bullshit coming out of their mouths. But, even then, they have to convince others to vote for them and then vote with them. That requires skills like negotiation, and persuasion, much the same as sales. Though, politicians probably have a greater emphasis on public speaking.