NSA is infamous for illegal and unconstitutional mass surveillance.

what kind of risks are there with buying a second hand phone? I don’t know so much about how phones work. But for example with a laptop they could in theory implant all kinds of hidden spyware and backdoors in the firmware and it would be impossible to find it and remove it. The only protection against that is that we believe it’s so unlikely someone random would do that. So that is just an example what I’m talking about when I ask about what the risks would be when buying a second hand phone?