I think Swappa and eBay have buyer protection if the phone is not as it is advertised. I've sold every iP that came out since the 3G about 10 years ago. All were ATT and I'm guessing the first 5 were locked to ATT (sold them that way). Unless you're buying from a friend, I think it's safer to go with eBay or Swappa.
As to water damage, I seem to remember the X was resistant to water up to around a meter. If you look into the bottom charging port, you shouldn't see any "red".
As to water damage, I seem to remember the X was resistant to water up to around a meter. If you look into the bottom charging port, you shouldn't see any "red".