sex.com has been stolen in the past
While this is the most famous example, other valuable domain names were sold at some point, and not always recovered.
You have to figure out for yourself who the rightful owner is, and whether the person controlling the asset is authorized to sell it. There have been instances of rogue employees selling domain names owned by their employers.
A good example would be sofa.com if I remember well.
Unfortunately many companies do not track their digital assets like they should, the whois record is often outdated and in the name of somebody who left the company long ago, domain names and websites are literally on autopilot, with nobody formally in charge. Mergers can further blur the chain of ownership etc.
Due diligence is important.
I would not buy a domain whose ownership is still disputed/unclear. If it's been stolen I must know all the facts to make an informed decision.
Just because the name has been returned to the rightful owner does not mean it's the end of the story. A stolen name may have been flipped once or more in a short period of time, so the wronged parties might fight back and sue. They will go after whoever is in possession of the disputed asset. You'd be caught in the line of fire.
If you've followed the Booth/Rebecca saga you know what I'm talking about.
Document the domain history as much as you can, especially when there is a lot of money at stake.
Then it depends when did the theft occur, was it last week or in 2000.
And also how was the domain recovered, through a court order, or mutual agreement among the registrars involved. The reasoning being that a court order is harder to override than an agreement among registrars. They could even change their mind. Again, refer to the Booth/Rebecca saga for details.