Keep in mind that someone doing this could always just have a low rolled version of the item, and then give you their lower one while claiming it was the one they just rolled.
If you do this, make sure that you have them drop four 2x4 items and one 2x2 item along with his cube while you are both away from your stash.
Gear is equipable of course so they should show the item(s) they're wearing in the slot that matches the base being rolled as well.
*(Not an acussation against the OP, just some thoughts on protecting oneself if they want to *sell* their roll in this way.)