i've got a few little overly trixy ways to do it for fun haha
down air actually does really well vs marth if you cant get on the ledge yourself because of that little knockback spurt plus his up b likely wont hit you that way
also you can dtilt, but aim so the 2nd hit hits him if he sweetspots, its hard to time, but the first hit will get em if he misses the sweetspot and for some reason they think they are much safer than they are after the first swing also, but it should hit if you time it right and they sweetspot, also his up b cant hit you if you do that as well
get up attack into back air semi spike works of course
if they are recovering high he has lots of options, he can just swing as you approach, in which case you just fake back then punish him, he can stall with over b and at high enough % an up air will get him, same with if he double jumps
but he can also just cram a dair in your face or whatever else, i dunno
marth can be trixy, but its not to hard