My mom and I ignore all calls that we don't recognize the numbers, names, or locations of, via caller ID. Yes, I know CID can be spoofed, and I do check out strange numbers online to see where they really go to. (On some of the call-discussion sites, such as Mr. Number, people have had numbers show up that are not valid to use in North America, such as the exchange prefix starting with a 0 or 1.)
Even though our mobile and landline numbers are registered to the Do Not Call Registry, the registry is pretty much useless since apparently, everything is exempt from its regulations. The calls that I've checked out usually are from "lower your credit card payments" companies, home security system sales pitches (even though those calls claim they are not sales calls), and Medicare back brace scammers (since apparently Medicare sells patient info that should otherwise be confidential, and my mom is on Medicare.)