I have a friend that sells on eBay, higher end bikes, and he often sells the item before the end of the auction.
eBay doesn't seem to mind, as long as they get their cut of whatever the price was, as does PayPal.
My friend says, with higher end bikes, the winner only wants the item half the time, so he's more sure of the lower sale.

Your second scenario is either a shill bidder or one of those bidders who bids on tons of stuff and then reneges on whatever he doesn't want.
There seems to be no penalty for this, and it's up to the seller to report the bidder, which they rarely do.

Sounds like an earlier bidder made an offer and it was taken, probably locally, which is odd, but with bikes, not having to pack and ship is a big convenience.