Well I play some Marths, and they generally edgeguard with Dtilt on the edge a lot. If spaced properly, it hits below the ledge, and knocks them back, forcing them to use their Up+B repeatedly until they sweet spot. If they're a space animal, they're often dead.
Of course, since I use Link and Doc, a more preferred method is to hang off the edge, and jump off and Back air. If they spike, then it's usually kind of like a ledgehopped dair. I don't see them do it off of the stage too much, generally off the edge, but I personally am not sure if that's just a preference or what.
Marth and his mean edgeguards.... bleh.
2cents
EDIT-Cookiez reminded me about the Fsmash. I generally see it used in combonation with the dtilt, because people love to get anxious and come above the edge when getting Dtilted, and thats when Fsmash comes in.