See yesterday's Washington Post for an article on the "check overpayment" scam.
I'm not sure 10 days is enough. The Post article says the scam hinges on common misunderstandings about the check clearing process. Just because funds are credited to your account does not necessarily mean the check is legit, and you could be liable for returning the money once the fraud is detected.
When I got a suspicious "cashier's" check, I called the bank and described it. The number sequence was not a valid check number, and they did not employ anyone with the name that was signed. The buyer never gave a legitimate phone number, either.
Be sure to report all suspicious information to the "issuing" bank so they can alert tellers to look out for certain signs. Then maybe they can shut down a transaction before funds are moved.