You need to either work on your own terms if the player can't be trusted or forget the trade. The best you can do is recommend they come to you and you're in a secluded protected area.
You decide how you teleport and it's your responsibility, if you're accepting requests and getting your ass handed to you then you're the only one to blame.
killed player reports, admins say that "it didnt say no kill" and it gets either locked or ignored.
I hated this. Learn to play survival.