For the DIY people buying second hand phones I strongly advise to get it yourself instead of buying online so that you can make sure that it is possible to unlock the OEM. So many phones are OEM locked by telcos (e.g., Verizon) and Graphene OS cannot be installed on them. So better checking in person (procedure explained in the Graphene OS guide) or buy from @abhishandy who will do it for you (i.e., find the phone and install the OS)