My caller ID on my landline is pretty accurate. If I don't receive a number, I don't answer it. If I see a number I don't recognize, I look it up on a site like "findwhocallsyou" or something similar. If it's legit, they usually call back within a day or two. I have the Ooma VoIP service, so I can block numbers that are robos, spam, solicitations, or what have you. I know many of these are spoofed numbers, but I do see a nice decrease in robos.
As far as my cell, if the number is not in my address book, I don't answer. I don't give out that number except for people I trust. There's also a robo/scam filter built in, so it informs me a "scam likely" message instead of the number.