Although I am on the TPS register (no sales calls) I am always polite to the sales people - it's someone doing a job, probably a job he doesn't enjoy, and who otherwise would be on the dole.
I am always polite right up until the point where I say, "Thank you but I'm not interested". If they respect that and then hang up all is well.
If they insist on continuing, then I take that as an invitation to have fun.
I am, however, never polite to the liars and thieves who claim to be from Microsoft. They deserve nothing but contempt and probably worse.