If it's a domain bought by a domainer who does a lot of outreach and who is now selling it privately on NameJet, then he has likely contacted everybody who might buy. It's a squeezed lemon. You might even be bidding against some of those end users ... with a few of the domainer's buddies pumping up the price too.
If the domain has actually expired, then you're a little bit safer but not safe.
You'll have to use your own judgment. Like gilescoley says, it really depends on the domain and what it's worth in the long term.