by the way power connectors are designed. It's impossible for it to be connected wrongly. So, I think most probably one of the power pin was connected wrongly which is the fault of the seller. He probably modded the molex or something and did not connect back correctly.

so now which molex is connected wrongly? The small molex for floppy or the normal molex for dvd/hdd.

That is not the small molex you use for display cards but it will be affected because if I am not wrong, the molex will loop from first to last with big molex, big molex then small molex. Therefore if first molex wire is connected wrongly, the second and third also wrong. That's why his dvd and hdd got burnt.

For the seller, I think he was lucky that when he tested, he was probably using the other small molex that he connected back correctly on the display card. Most branded PSU have at least 2 small molex.

But then this is based on the information I gather from what the seller and buyer gave. Not standing in either person's side but in this case, seller seems to be more at fault.

Making mistakes is one thing and taking responsible for mistakes is another.

If I am driving and made a mistake and knock someone dead. So, I say sorry and no need to pay for my mistakes?