Some advice please....questionable check from craigslist???!

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My fiance and I just bought a new tractor, so we decided that we are going to sell our old one. It's a 1990 old craftsman tractor. It still runs, and in fair condition with a snow plow. So we posted it for $500 obo. Well we were contacted by someone about purchasing the item. It was strange though, they wanted to send us $3,200.00 for the tractor. They said $600.00 for the tractor, and 2,600.00 for the shipping, in which they wanted us to cash the check, then western union the money to their shippers. I told my fiance something seems weird. Well today we recieved the check not knowing they were sending it, and it just seems weird. The cashiers check ends up being a business check, and it says it is from florida, but the ups shipping starts in California. The person has never given us their information, no name, number, all we have is their email address. We tried checking with the bank in which it came from, they say it is a legit check, but reports of fraud have been listed on the account. We have another person who wants to buy the tractor, and have given us all of their information, and seem more legit. But we are waiting since we already have the original interested parties check. What would you do in this situation? Should we take the check to the bank to have it verified, or destroyed? Should we just send the check back if possible? We are both just confused, and wondering if it is a scam. Ever run into a scam like this? Please give any and all advice.