There's usually an auction after expiration. Domains don't just become available again anymore.
And all sellers with parked domains seem sketchy, so that much isn't a surprise. If you do intend to buy a domain, definitely do so with a third-party escrow service.
Over the past 15 years I've turned down multiple offers of $5000 for a number of my domains.
If they had been for the right domain I would have jumped at the opportunity, but unfortunately they've always been for ones I'm more attached to and using for one purpose or another.
Back in late 2005 or early 2006 I also had the chance to buy a certain domain for around $10000 and passed. Today I'm still kicking myself - lightly, but still. If I had to do it again, I would have forked up the cash.