I got one of those fraudulent EBay messages today at work. The one where your account is being suspended. Unsolicited Paypal messages, same thing. Avoid them.
EBay may send you promotional email that is real. Anything to do with your account requires you to log in to "My Account". That's where they send all messages involving the legitimate transfer of sensitive information and pertinent account information. So the rule is; if you didn't go looking for it, and it's not purely promotional, it's probably not real. I think they might offer Sellers the ability to set up messaging or email notices directly from their account to their designated address(s)/devices. Not sure on that though. If so, you'd verify those and respond by simply logging in first. Won't cover all the fraud, but will the vast majority.
Nothing new on the cheap fraudulent tractors. Almost always there. Also, the Western Union, etc. pay methods, as was mentioned, are a red flag.