Well, it was in there for a reason.

Why?

Because It was probably someone's stash of money maybe for emergency, and they forgot to remove it when they sold you the game system(s). If you take the money, just think of how anxious the person could be, and what a relief if could be if you returned the money. I know some people are thinking it's a dog eat dog world and if they leave their money, it's their fault, but why not a second chance? I know I'd be very thankful if someone returned money to me I lost.

Even if I though about doing that I would be the person that forgets where the yard sale was or discovers that much later on.

yes
i think you are