Definitely scam.

They're not after the free bike. They'll intentionally send you a check for too much and then send the difference to their "shipping company" via Western Union. They'll offer you a premium for doing so.

In the end, you'll have sent real funds to the scammer via Western Union, and they'll have sent you a bogus check. Beware, as they're using bogus USPS money orders these days.

Bottom line, it's cash or Paypal these days. And, you still need to be careful of bogus Paypal email scams.

These scams take other forms as well. My wife does interior decorating work and answered a CL listing looking for a painter to paint their apartment. The scammer said that they lived overseas and wanted to have the work done before they moved in. They immediately responded to my wife and told her that she had the job, and requested that she provide our address so that they could mail her a pre-payment.

I immediately told her it was a scam. Not sure how it would've worked out, but I'm fairly certain that it would've involved wiring money to the landlord.

Beware! Vultures, vultures everywhere!