gah, your word on how skillful you are means nothing, 'this is the internet', everyone is an expert on everything once they're behind a keyboard.
You buy something and it doesn't work, you don't open it, you return it. its as simple as that. If I sold something and the buyer comes back to me saying "its broken, I opened it to check" they get told where to go.
The unit has been opened, that doesnt mean the seller is aware its broken, they may have bought it s/h and never used wifi. I bought a DS off a friend years ago and the mic didnt work, he was totally unaware since none of the few games he's played use the mic.
And 3 days is NOT long enough to jump on the negative feedback button, the seller may have a life and not sit over his email inbox, there are endless reasons for not replying within 3 days. I am sure the ebay recomended time is 5 working days.
Its people like you that make ebay a pain in the ass to sell on.