Free Agent Fraud

the game of baseball witnesses players changing teams almost weekly. some big name guy goes here for millions of dollars while another big name guy goes there for draft picks or prospects. is all the trouble worth the benefit though. in some cases yes, but in some cases no as well. we've all heard of those big deals where a player gets signed for a ridiculous amount of money because he had a great season the previous year with a different team. what happens when they don't perform? was all the off-season work worth the mid-season flop? how do managers draw the line on whether or not the benefit of taking a chance on a player outweighs the work they put in and money spent to get him. it doesn't seem likely that we will ever find a way of knowing the future, so what factors do managers have to look out when determining their overall costs and benefits of taking a chance on the new free agent?