I would not trust Cohen at face value also;as much as I despise Trump I would demand more evidence before aacepting what Cohen says as the truth.
Most informers and people who turn state evidence are slimeballs who are doing so to save their skin. Sonny Gravano..the underboss who sunk John Gotti in court...as pretty slimy himself.
I think someone in Finland is being very naïve. Any D.A./Prosecutor will tell you that most witnesses you use in bringing down big time criminals are pretty slimy themselves.
And Cohen has made the point that his testimony here is unlikely to reduce his sentence. He doesn't seem to have anything to gain, apart from blaming the bigger crook.