My rule of thumb: Block if you do not recognize number or it is within your area code but no name associated with it. Block if caller ID is just the name of a city and state. Block all 800 numbers with no caller ID. Let caller go to answering machine and if no message is left, go back and block number. Because I have a business, I've had to block upwards of 10 calls a day or more. If you do answer, be on high alert and at the first indication the call could be a scam, hang up and immediately block the number.