In the postseason Scherzer was actually really good as he managed a 3.77 ERA in 14 innings, and his most famous moment came when he demanded John Schneider to leave him in the game. Throughout the whole season those numbers weren't nearly as good, which is why teams should be cautious before signing him.
Not only did he not perform well, he did not start very much either. He didn't offer quantity or quality, which begs the question why would anyone sign him at all? If teams are only going to base it off his psotseason outings, then they better have a really good existing rotation already, where he can slide into the 5th slot with no pressure. Either way it's a big risk to sign him.