On all other selling platforms it is the seller's responsibilty to up to the point of delivery regardless of insurance. Ive been on eBay for 24 years 2000+ transactions and have 300+ transactions on Reverb in the last 2 years. I've seen and experienced it all from both sides. The seller is being an asshole because he knows there's no way for you to get the money back without his approval. If he doesnt give it back I would post his info so no one else has to deal with this person.
-- obscuremachines

One very important distinction between those 2 you mention and MG using uninsured shipping + PayPal F&F is precisely the responsibility of the seller being engaged by the terms & conditions everyone agrees to prior to the deal, as opposed to here. As far as I know, both these platforms retain a portion of the sale money in order to protect the buyer until receipt, which could have been done here as well using PayPal Buyer's Protection.
Basically, a selling platform isn't the same as a classified ads section, in the latter the user is responsible for most of its security. If that same deal had happened on Modwiggler instead, I'd wager it would have gone the same way, for the same reasons.

If we're talking morals though, I personally would consider splitting the loss instead of covering the whole amount because that's what F&F means to me, as in if this happened between me and a friend of mine, we would definitely split 50/50 I think. There's also the question, which I think wasn't really cleared out, of whether the seller offered insuring the shipment and was turned down or if he/she didn't mention it at all and then says "you didn't ask for insurance, sorry, too bad for you" - first case is on the buyer, second is definitely on the assholery side :-)

Also, to be clear, linking a user name to a bad reputation in the thread created for this is totally fair game when the dust settled and one person feels they got a bad deal, but I wanted to say that posting personal info (e.g., names and addresses) is a bad idea and could land you in legal troubles.

@lazarusgordon I would suggest to wait for the result of the enquiry started by the seller, and if it doesn't succeed, you can suggest to use a State Mediator by sharing this link with him/her: https://www.service-public.fr/particuliers/vosdroits/F11064

Best of luck, I really hope La Poste finds the lost parcel soon so this ends with smiles and patch cables !

--- Voltage control all the things ---