The one heuristic I try to keep in mind whenever dealing with anyone on the phone is “if they called you, they want something from you”.

Even if this isn’t true, and someone is calling you out of the goodness of their heart, for reasons beneficial to you, if you treat everyone who calls you with the same suspicion you would treat a cold caller on your doorstep, that’s a good way to get yourself in the correct frame of mind to avoid getting scammed.