Play some games with the scammer.
Tell the buyer that you will only sell them the bike if they pay for and organize the delivery of it.
If they agree to that get them send you the 'check' addressed as
'General Delivery' so the scammer doesn't know your postal address.
Get a bike box from a bike shop, put 15kg of rubbish in it, seal it up well and organize for it to be picked up from somewhere that isn't your address.