"Seam-picking" probably wouldn't work unless the pitcher had a razor concealed in his hand. He can try to "nick" a little piece of leather off the cover with a sharp fingernail to form a little "wing" that will make the ball jump.
He can also put a little dab of Vaseline in his hair that he can transfer to the ball, a little bit of Crisco shortening just inside his collar that he can get on his fingers, or a little blob of black axle grease on his uniform belt ... if he can get that onto his hand, he can throw a "spitter" that doesn't spin gyroscopically and jumps around on its 90 MPH trip to the plate.
If the catcher even suspects that the ball is "moving" more than it should, he'll hand it to the umpire after a pitch. The umpire will give it a quick going-over and either hand it back or put it in his "reject" bag. If a baseball even touches the dirt, the umpire will automatically reject it and toss out a new ball.
The average professional baseball game uses up about 90 baseballs, the rest of which go to practice or to Little League teams ...