noy true person above,
on kino I have often ended up runnig between two boxes during yard sale and getting the same gun again having just picked it out the previous box.
e.g buy random,
run to other box,
buy random, run back and pick up the gun,
buy another random from it,
then run back to the other box and pick up gun,
then run back and pick up the gun again.
sometimes you end up having a gun you've already picked up, so it's more than likely this is possible.