The Check Scam (fake or bad checks):

• A "sub" sends a check or cashier's check, often for more than the agreed amount, then asks you to refund the difference or forward money elsewhere. The check can take days or weeks to bounce, long after the bank shows the funds as available.
• "Funds available" does not mean the check has cleared. Banks must make deposits available quickly, but you're still on the hook if the check is later found fraudulent.
• Red flags: an overpayment with an urgent refund request, a check from a third party or business you've never heard of, and pressure to act before it "settles."
• Safest approach: don't accept paper checks from strangers at all. Stick to payment methods you've vetted, and if you do deposit a check, send nothing back until your bank confirms it has fully cleared, which can take weeks.