ECN Forum Forums General Topics of the Trade General Discussion Area lightning damage?

I received a call from a home buyer about a 10 year old home they are in contract to buy. The home inspection reported that each receptacle throughout the house has burn marks on the top slots only. I have not gone there yet but I thought I'd see if anyone has seen this before. The seller says they don't have a clue about what happened, it was like that when they bought it. I am thinking maybe lightning, but why only the top slots? Maybe thats where stuff was plugged in? Also, since I have not seen it yet, it is possible that it is not every single receptacle, altho that is what was reported. It is also possible there may be some burned on both top and bottom.
Only idea I could think of other than lightning was something like a large appliance used regularly throughout the house, like a space heater or two.

Maybe the inspector was/is mistaking a dirt build-up on the devices for burn marks?

Ever see the "soot" trail above a plug-in transformer that has been around a long time?

Also could be loose connections on the screws (or backstab?) leaving heat marks?

A peek inside the panel would reveal lightning damage.