I answered this in post 4, above, and Urs Max corrected me in post 5. According to Urs Max, you could drum this matter through the courts, but oh, that would take a great deal of effort and costs.
Second-hand goods are deemed to potentially include signs of use, or wear and tear, and private sellers are not regarded as having the same capabilities as professional sellers. So when the seller said he could no longer sell to you as he'd realised that the equipment was defective, an outsider, such as a Court, is likely to think the seller sounds fair and pragmatic, and that he provided a reasonable explanation of why he could not deliver.
This will still be so, even if you were to show that he advertised the same item later. This, if for no other reason that that you can probably show, at most, that it was a similar item, but you're probably unlikely to be able to prove that it was the identical item.
You hadn't paid him, so you haven't lost any money. That's good.
You didn't receive the goods as promised, so you lost the potential to receive the goods as contracted.
"Compensation" in Switzerland is regarded, in general, as being only to restore unto someone what they have lost, materially . Therefore, if there is a case, it is only to be about the loss of the item, itself, and not for anything additional, around the blank sale.
Therefore, it would be most unusual and is very unlikely for anyone - especially not at this level of transaction - to be provided a financial settlement to compensate for aspects such as inconvenience, emotional suffering of disappointment, sorrow or regret, for help to recover one's dignity, for days on which the person might have had to get by without having the item they had hoped to purchase, or for the costs of the mails, letters and and phonecalls involved.
If it were me, I'd probably be annoyed, and would make a note of that seller's name, so as not to transact with them again, and would then turn the page and look for another item that seems more or less to fit the purpse. I'd much rather do that than fight my way through a Court system which isn't built for this kind of dispute within a culture that, in general, finds the "compensation" notion odd and often a little nonesensical.
I'm not saying you don't have a right, as I think Urs Max is correct that you do. I just would never want to sacrifice my free-time and nerves for such a cause, knowing that you're unlikely to win, from it, neither a shiny new TV, nor that particular TV that was not sold to you, nor enough money to buy an equivalent item new, nor any "pain and suffering" type of compensation.