It seems that my example was poorly chosen and mislead you however; the initial point still stands: chose someone that you both trust. I was typing it in a rush and I didn't think anyone would spend the time to pick at small pointers.
Yes, a level 400 can deceive you, and so can anyone else. With the logic you applied, anyone can be deceived. In these forums we even witnessed someone who often dealt with myshop trades and happened to be a well known player scam.