Looking to buy the pixel 7A seen one used online for cheaper is it safe to buy or better off just buying new for cash via Argos or something along them lines.

    If the used one is OEM unlocked, you can go for it.

    nuclear
    Safety wise, I believe that installing GrapheneOS will be like a factory reset; and things are designed such that you don't need to worry about any lingering malware on a boot partition/loader ( like you might with a PC disk).

    With a second hand phone, you need to ensure the phone can be OEM unlocked:
    https://grapheneos.org/install/cli#enabling-oem-unlocking

    Useful discussions here:
    https://discuss.grapheneos.org/d/3719-oem-unlock
    https://discuss.grapheneos.org/d/10362-oem-possibly-carrier-locked-phone/5

    Argos, is that UK? You should be OK:
    https://discuss.grapheneos.org/d/6809-uk-carrier

    So just get the seller to confirm it was a UK/EU sourced phone and not from USA.

    In Android Settings > About Phone > Battery Information there is a battery 'Cycle Count' number displayed. I'd ask the seller give you that information - or be suspicious if they give excuses "too hard to find, too busy" etc.

      Swappa.com can give you reassurance that the OEM unlock is guaranteed.