On occasion, I have seen legitimate phone numbers that were spoofed by telemarketers. This happened recently with a power company in San Diego. Legitimate callers will always leave a message and legitimate callers understand that many people are reluctant to answer their phones.
These people have called twice this morning. CID was SEMPRA - no message was left with either call. Have now blocked their future calls.
Sempra is the same as SocalGas they keep calling me letting phone ring once ...it is annoying i'm about to call them up and change my number to my JUNK call number that i give out. where i can block people who are silly but mostly I never even hear it.