My strategies are as follows:
1) Take advantage of other tilts (already elaborated)
2) Take to the air. Short hop fairs can be really useful, as could jumping past somebody and using a bair attack. Just change up your style.
3) Embrace it. In the right situation, you can combo with them really well. I've had a number of people get caught off guard by an fsmash combo. What I do is as follows: Dash attack to hit them up in the air, fsmash, dash attack again right before they land, fsmash again, etc. You can tack on massive damage really quickly (70% comes faster than you think), and if you keep the pressure up with short hop nairs or wavedashes out of their attempted combo killers, you should be able to press them to the very edge and use his dair for a smooth kill move.
It's all about knowing your options and spacing him properly.