It depends on your opponent and how they move.
However in a more typical and match-up oriented sense you have a few options besides baiting.
If your opponent is dash-dancing you need to overshoot your shffl'd Nair so you don't miss and get grabbed.
This also works for grabs, but you'll suffer more lag if you miss- in the event that you do miss you can try shining or spot-dodging the punish.
You can also run in and wave-shine, this can be harder to hit with but you can follow-up with an Usmash or grab. It's best used as a punish.
If your opponent isn't dash-dancing you'll have to improvise and space so that you're outside of Fsmash range at least- this counts for most of the match-up until you find an opening.
Answers aside, I personally bait with my movement until my opponent whiffs and then I punish.
The reason people play the match-up like this is that Marth can evade with his wide dash-dance and out-prioritise your short Fox limbs with his tilts.
This doesn't mean you can't be aggressive, once you've you're in you should go ham- just make sure you're not gambling your stock with an approach as it's never in your favour.
