I don't know if this is common knowledge, but I ran out of change for parking meters and I had several one dollar bills, so I put a dollar into a vending machine and then asked it to return my money. Vending machines only return coins, so it gave me four quarters, and I could pay the parking meter.
I bought a Nokia BH-501 bluetooth headset from Newegg some months ago. One of the earpieces broke off of the behind-the-neck band about a week later, and I never got around to investigating the warranty, etc.