To expand on my past post, Link's OoS options are really bad, and he is often forced to roll more often OoS, because it's not particularly safe for him to do anything else once you've established a good position on him. More than likely, Link will choose to roll backwards, cause it gives him more breathing room, but honestly this is such a win win for you because he also loses a large chunk of stage. If he tries to roll through you, I'd suspect that he'd be vulnerable in most cases, so always be on the lookout for him to roll through you, and just don't worry if he chooses to roll away from you.
If you grab Link, and he's at a percent where you can't get any sort of guaranteed combo on him, always throw him to the closest ledge. Getting him to a ledge forces him to engage you, and that goes way in Marth's favor. Since Link is quite slow, you should be able to maintain stage control like this for most of your match. Much like what I've said above, throwing Link forward, or backward (via downthrow, not bthrow) will lead to a tech chase. The same applies. In most cases, most Link players will want to roll away from you if given the option, although they will also occasionally make a gambit to roll through you. Your best bet, IMO, is that you always cover the roll through/tech to stand option by walking towards Link and then responding to his choices afterwards. If he techs to stand, you should be in position to mess him up already. If he tries to roll through you, you have plenty of time to dash the opposite way and grab him. If he rolls away, congrats, he just gave up almost half of FD from your throw plus his back roll.
You might say to yourself, "Well if I get a sweet read that he rolls back I could do -insert awesome thing here-." Don't let those thoughts dictate the match, because them rolling back is already a plus, and by going on a guess (even an educated guess) you open yourself up to punishment if you guessed wrong. Also, any and all stage control you have gained is instantly reversed if he rolls through you and you run after him in the assumption that he rolled away. Suddenly, you are now the one pinned close to the stage and Link is now in a good position to force you to act, plus has tons of stage behind him to projectile spam. So take your small win on the roll back, and just walk forward to close as much of the gap as you can and continue pressing Link closer and closer to the edge. Trust me, by doing this your opponent will literally feel like they can't do much the whole match, even if it's actually really close!
In neutral, watch out for Link's grab. I find that my optimal dash dance length is such that I sometimes get caught in the hookshot, but at the same time it's a huge risk for Link if he misses. In the event that Link whiffs a hookshot grab, do not force anything. Don't go for an fsmash that you don't have time for just because you really want it. Take what you can get naturally, which in almost every case the worst scenario would be a grab, and honestly that is just fine.
