Humidity from the shipping process can curl cards slightly but should revert to normal after a few days. This type of curling should be very minimal however. Anything more might indicate a different underlying issue. Please open a service ticket if that is the case and we will gladly assist you!
Additionally, supplementary products (*) foils are known to curl heavily and not accounted for in their grading. These cards are generally not tournament legal for this very reason and all concerns should be addressed to the company(**) directly. This should not affect regular set foils.
*Supplementary products includes, but are not limited to:
Commander Decks Foils
From the Vault, Secret Lair and Premium Deck Series
Special sets (Commander Legends, Modern Masters, etc)
Pokemon and Yugioh Tins exclusive promo
Pokemon boxes exclusive promos
Some other FNM/league cup promos
** Outside customer service links