Anything involving shipping, cheques, money orders, web sites, dealerships, or online stores is a scam. Anything with lightblue, azure, size=1, or other attempted hidden text is a scam. There's a few other scams that are a bit harder to spot, mostly involving newish cars and motorcycles priced abnormally cheaply. Otherwise it's just like any other classifieds - meet in person, and see if it sounds like he's trying to rip you off or not. Anyone who won't meet you in person is likely a scammer. Some people will insist at meeting at a store, mall, etc out of paranoia, but those are exceedingly rare - most sellers will just give you their address and a good time to stop by so you can take a look at whatever they have. Anyone who even mentions shipping, money orders, etc should not be contacted back, unless you're in the mood to do some baiting.
--Bushytails