It can be difficult to pull off in certain adventures without your players noticing, but I always just lower the amount of treasure they receive from future encounters until I have "cheated" them out of an amount of gold equal to the amount they looted from Dead Fred. If I am irked at them for looting Dead Fred because it was a metagaming decision that violated their characters' personalities, I actually penalize them gold over the long run. The heroes are stronger than they should be for a brief period, but it evens out over time.
I've never explicitly stated that I do it, and my players have yet to notice. However, our handling of treasure makes this easy to do; it may not work well for certain low treasure/extremely high treasure campaigns.
I've never explicitly stated that I do it, and my players have yet to notice. However, our handling of treasure makes this easy to do; it may not work well for certain low treasure/extremely high treasure campaigns.