If you see the copper color on the outside edge of the coin, then it is just toning. (That color will be red) If you don't see the red copper layer on the outside edge of the coin, then it was plated. If it were missing cladding, it would be the color of the copper layer. Just looks altered/toned in circulation. The real color for a missing clad is this drastic:



Red color, not brown as that is an outdoor find.

On a missing clad on one or both sides, look at the example above, the strike will be weaker. So you should have taken the money and run. But now you what to look for on these.
CoopHome:
Take the money and run, or keep another from buying something that is not worth the loss to them. Education is vital. He might have a coin that you might want to buy some day. Breaking the ice now, may pay off more in the long run.