Why do people think these guys are so good?

I'm talking about nba players who get buyouts. Like PJ Brown and Joe Smith. People have been talkling about smith for months going to boston. he gets released and immediately joins the cavaliers? He averages 5 points. I'm sure there are plenty of ppl just as good. Also with Pj Brown last year ppl nonstop talked about him going to the celtics and him doing good. Where do these rumors come from? Like the ones about joe smith, PJ Brow, and Stephon Marbury. How did ppl know they were going where they were going?