Is there any danger to use a second hand hardware wallet ?
There could be, if the user is a smart tech savvy person he could reprogram the firmware of the device and steal your coins.
It's always a good idea to reflash a second-hand hadrware wallet before using it.
Yes, it's best to reflash the trezor or hardware wallets. If it supports third party softwares and if the old owner is a techy then it can be easily manipulated. It's best to buy a new one.