You call the bank that the check is written from. Tell them you are a Vendor wanting to Verify funds on a check. They take your Name/company name, then the info off the check. They look it up in less than a sec and tell if the check is good. Just be professional, and lead off with your business name.
They will ask how much the check is for and for what account number, name on the check. It is really simple and fast.
Then you know, take it to the bank right away.