hope you complained to Mercari. that is almost a 10 year old laptop.
it seems there were several models of the MacBook A1342. so you may need to search using the serial number/device id to get the proper hardware needed to get going. hope it is on the case somewheres. if you have the info, the following site will help.
https://everymac.com/ultimate-mac-lookup/
I attempted to buy a HP 14 laptop, from Mercari, for $80 recently. Instead I received a MacBook A1342 with no charger and a sticky note saying it was missing it's RAM/OS/HDD.
I can't get my original item or money back.
Would I need to spend more money to get it working? Before I shell out another $20 (charger) on a beat up old laptop I'm wondering if I basically got a junk laptop. I don't know what missing RAM/OS/HDD entails, but maybe it's nothing and $100 turns out to be a good deal.
Any help would be appreciated. Thanks.

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