Hi there, I'm considering buying a used Verizon Galaxy S4 and I'm trying to determine what are the key points to know. I am seeing a lot of discussion about the different bootloaders, different kernels, different android versions, etc. It seems like some phones cannot have the bootloader unlocked and some phones can't even be rooted. Can anyone explain that to me so I know what I should be looking for? In addition, are there any especially pervasive hardware or software bugs that haunt the S4? Thanks!