Super easy to spoof a number. Just don't answer. Period. Don't decline the call, either. Just silence the ringer and let it ring until it goes to voicemail. If you decline the call, it goes straight to voicemail right away. Here is why that is a factor.
Every single thing about that phone call is logged. How many rings? Did you answer? Did you decline? Did you press 1 to speak to an representative? Did you talk to the rep? Did you purchase the extended warranty? It's all data that they use to sell. It's all about your willingness to interact. Your phone number has a "score" attached to it which they can sell for profit. Phone numbers with a high score bring more than those with a low score. The point here is not that they're selling your number. Even I already know every single phone number in the US and Canada and so do you. The saleable item is the data point between your number and the score.
If you decline the call, it's a data point. If you answer, it's a data point. If you press a key and interact with the phone call, it's a data point. If you just silence the ringer and let it ring until it goes to VM, there is NO DATA POINT. It tells them nothing. There are two absolute worst things you can do: 1) answer the phone call to speak to a representative to have your number removed, and 2) obviously, purchase whatever they're selling. The more you interact with these numbers, the more spam phone calls you'll get. Just ignore, let it ring, and don't do anything.
That certainly won't make them stop calling. Phone numbers are just numbers. Even if you include every single numeric digit from 0 to 9, there are only about 90 billion combinations of digits which cover every single possible phone number in North America. Narrow that list down by entering the 350-ish area codes in North America, and you limit that number to about 3.5 billion possible numbers. That is something that a computer can generate and call in a matter of milliseconds. It's not that there is some magic list that says Sine_Qua_Non sounds like a good target, let's look up their phone number and call them. They call EVERY number. My 15 year old nephew gets calls about his extended warranty, and he doesn't own a car nor is he old enough to drive. They just call everything.
Their computer calls every single number in your area code over a certain period of time. Then it logs all the interactions each number has and sells the data. They will usually spoof a number in your same area code and exchange so it looks like a neighbor is calling. You are many times more likely to answer a local call than a distance call, especially if you're older. I live in PA but I have a CA number, so most of my calls come from an 818 number, and usually during PST business hours. They're assuming I'm in CA.
The thing that gets me is... this can't be profitable anymore. Data points bring big money (as of 2018, data surpassed oil in value globally) but the whole spam calling has become so out of hand that the number of people who would actually fall for it is next to zero. Given the hundreds of spam calls I've had over the last couple years, and the fact that "vehicle extended warranty" has become a punchline, I can't imagine that data-only pays their bills. And what is my data point worth from these calls? Even if they collect my interaction data, sell it to another robocall company, then they call and collect my data.... and if that has happened 100 times, where is that value? It's the same basic data set over and over.
According to Forbes, the average person's social media data is worth about $65/mo, but over time it decays and becomes stale. After the first year of your FB, twitter, or Instagram profile, you might only be worth $40/mo. That is why the social media platforms are constantly evolving. That's why you get clickbait websites thrown in your feed. You can choose which ones you like and dislike so it tailors your experience, but in reality... they're just finding ways to collect more data and put one last squeeze on the lemon.
