Previous owner hurt himself on the ATV my husband purchased the day before...

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My husband purchased an ATV from a man and a bill of sale was obtained. My husband doesn't really know much about ATV's, he is just really getting into them, so when he brought it home it seemed to take off fast with just a little throttle. He called the guy the same day as purchase and he told him to bring it out and he would take a look at it. My husband took it back to him because if there was a major issue he would give him the money back. When my husband got there, the other man jumped on the 4 wheeler, hit the throttle, ended up popping a wheeley and falling off. He got up and ended up fixing the issue. Well, about 3 days later we hear through a friend that he had to have emergency surgery because he broke his back. Now, about 5 months later I hear rumors that he is talking about getting a lawyer. Can he sue us for this? I live in Illinois, and wasn't sure if we could be held liable due to a purchase period on these types of vehicles. Especially since he was trying to show my husband it worked fine, so he wouldn't have to give the money back and he hurt himself on his own property within 24 hours of the original purchase. Does anyone know anything about this?