I am sympathetic to these callers because they need to earn a living, but their employers have abused their rights to contact the general public at large in order to sell a product. I am TURNED OFF to sales people no matter who they are... and, when they call my home, it pisses me off even more.
You can block numbers, and you can put your number on the NO CALL list, but these assholes have ways to circumvent the rules and call your number anyway.
SO... don't answer or, answer and play games in the hopes that it will stop them... don't be fished in...