I posted an ad for my motorcycle for sale on a bunch of different motorcycle classifieds websites last week and I just received a text from someone who says that they want to send me a cashier's check for more than I'm asking for my bike. They want me to cash the check at my bank and then send them the difference. Then, they'll send their shipper to me to pick up the motorcycle. This sounds fishy. After talking to a few people, I know it's a scam. What should I do?