They are low, break fairly easily and some just remove them for service and don't replace. There are a couple "plastic" braces that run the length of the engine compartment that support the under-covers, so if they weren't replaced, I'd say no problems. Also take a look to see if the front under-cover is in place with all the attaching hardware. If all looks fine, have fun with the car.
I have a 14 and in 15, I hopped a curb I didn't see in about 10" of snow. Needless to say, it busted my skid plate to ****. It's been almost 5 years and it's still on my to-do list to replace. So even if the previous owner did jump a curb, I'd just chalk it up to one of those things you might never know about - had it not been for those receipts. If the alignment is right and everything is intact, then I would do as Turbonut suggests, have fun with the car and don't give it a second thought.