Thanks for the clarification.
So, the answer to the OP's question of,
"Can he unbind it via a web browser, without giving me his login details?"
is, "Yes."
The previous owner can unbind it remotely from a web browser with his login details...
No need to guess. The seller is clearly listed in the listing. Yes, all Chinese and all have terrible Critical Reviews. However, when it is listed as Prime Next Day delivery by Amazon, it is clearly already in stock in the U.S. in an Amazon...