While trying to not get too technical, the way a Spoof CID works, is there is a computer with VOIP software. This software allows the person to use their computer to dial a number out. The software on the computer will generate a number. This is particularly done with SPAMmers trying to get you to buy whatever product or service they want you to spend your money on. If you live in the US, and your telephone number is on the Do Not Call list, then it is illegal for someone to call you. Even if they are calling you from India, they are still not allowed to call your number. Calling you to solicit your business is illegal. And when someone does a crime, that makes them a criminal. In addition, spoofing your number to show a number that is not yours is also a crime. This means they are committing two crimes. Simply put, don’t do business with criminals.
A second option is they have a specific telephone number showing up. This is typically done with Scam Artists showing a trusted number, and trying to get you to let your guard down since it is a trusted telephone number calling you. In example, if they want to display Social Security to get at your retirement funds, they will show the caller ID to show Social Security, and they try to get you to provide your date of birth, and your social security number. Social Security, or law enforcement will not call you about an issue. If someone calls showing the caller ID as a trusted number, do not believe it. Instead, hang up, and call the official number of which ever agency that supposedly called you.