I say if he doesn't play well and add to your team's play, don't get him. Like Mullen said, you can have **** players who for some reason play great - I experienced this first hand after taking on an old irish right winger who was worse than my original one in BSN. We're in league 2 now and the old guy is still scoring goals/making assists and I let my original winger go a long time ago because he sucked. You can get the same effect with a good player who just can't play well for you.
However, do pay attention to three things:
1) His preferred role/position: the scouts will usually tell you what role they think he's best suited for. It's usually a good idea to listen to them on this (though not always). Example is when I signed a young winger who was supposedly amazing, but he would never make an impact. I was playing him in the MR position, which he was supposedly "accomplished" in, but not in his natural AMR. When I switched him to AMR, he became one of my best players. Same with roles when I put my CM (s) to AP (s) and suddenly he started playing well.
2) Your key squad skill. If your team plays a short passing game and has a high average passing attribute, then a player with crappy passing won't be able to contribute to the team as he'll fudge the passes when it's most important. If your squad is the heading type and he can't head -> same problem.
3) Some key mental attributes. I found that players with extremely low bravery end up being worthless no matter how great they are in other skills. They rarely try to dribble past - instead, they always turn away from the opponent and shield the ball (because they're scared) and either slow down the play or lose the ball altogether. Low bravery/decisions/positioning can really ruin an otherwise great player, so be careful with that.
If you're in the lower leagues, quickness is highly important, so make sure to note that too.
