In sports, especially before a trade deadline, misinformation is more common than information. Team sources and agents spread dubious rumors that they hope will give them an edge. Now the league office is involved because of the looming PED suspensions. As long as one recognizes that one is chasing rumor, innuendo and conjecture that's fine.
When one starts repeating a statement as if it is the truth or relying on a statement to support an argument or belief, one gets on shaky ground. This has happened several times regarding Cashman's statement that he was against trading Black for Soriano. That statement may be true. But there are reasons to take it with a grain of salt.
Since the Yankees are actively pursuing another bat, it is in their best interest to suggest that Black was too high a price to pay. When the Sox say, "Rios is better than Soriano, give us a better player than Black," Cashman can retort, "That was a bad idea at the time and now ownership isn't so desperate, take Evan Rutckyj.”
Cashman and the Yankees have an incentive to pump up the value of their own prospects in general.
The Yankees know that drama generates interest and may feel any attention they can draw away from Rodriguez is beneficial.
So while it's possible that Cashman was really against trading Black and he was completely aboveboard with ESPN, keep a healthy dose of skepticism when you're reading.