I give it 72 hrs - 3 days - refrigerated then freeze or toss. If it does not smell like fish at all, Cook some (cook it through) take a small bite. You will probably smell if it is off when you start cooking it in the pan.
Some fishes you find in the store, even sushi grade stuff that you can buy at places has been smoked quickly, which retains the color and preserves it a tiny bit, then it is vac sealed and flash frozen, then distributed. If your friends hasn't been vac sealed (I am sure he does not partake in this smoking or flash freezing) BUT he packaged it nicely (patted it down, wrapped in cellophane, and sealed it nice and tight in ziplock) plus kept it cold, again, cook a few ounces and see whats up.
I prefer pan seared M-rare but if your doubting it's freshness, I would just cook it through it would still be tender.
Not worth it if you think it is bad however. Spent a week in the hospital once (that was clams however, and about three dozen Gin induced pieces at that...).