Your question is not very clear, I hope you don't mean that hardware wallets are usually being shipped with some "default" seed phrases and passphrases. If you notice something like that, you should immediately withdraw your coins to a wallet you already have, break a bought hardware wallet with a hammer, and then throw away this malicious hardware wallet. If you buy a hardware wallet from an official store or retailer, the chances of getting a malicious wallet are slim, but you still should be very careful. Should you import your existing seed phrase into a brand-new wallet? It depends. If you feel your previous secrets haven't been compromised, then it would be the fastest way to transfer coins between different wallets. Otherwise, you will have a hard time sending coins address by address to preserve the privacy of your transactions.