Pre-owned / refurbished camera or lens

So let's say you travel in a foreign country and you desire a new camera, lens and memory. How do you tell pre-owned / refurbished gear from the real thing?
I know I am supposed to buy at a reputable store, look for scratches, original box, ability to return goods, good international warranty and even consult the photo counter in the camera. But sometimes the sellers can hide all these clues from me. Also if they see that my stay is short, they get more courage to sell me junk.
Any idea how to avoid these problems?