Ouch... I suggest you direct your Marth friend here to read and re-read the stickies. He spams roll and random F-smashes and dash attacks way, way, way to often, needs to learn how to L-Cancel, SHFFL and Wavedash (By learn, I mean implement into his game, not learn how to do the tech, which he can do). His spacing and edgeguarding was pretty appaling, tell him/her to always hit with the tip of Marths sword for the most knockback and the least chance of bieng shieldgrabbed. Also, try getting him/her to sweetspot the edge when recovering with Marth. DI was also an Issue, but i'm not so good at that so I'm not gonna comment on that lol.
Sorry If I sound a little harsh, but its difficult to rate someone who has so much to learn. Just direct him to the stickies here, and the improvement rate should shoot through the roof!