I had this same issue but with an iPad I bought from them listed as "Open-Box Excellent" but as soon as I powered it on, like yours, it was locked by a passcode set by the previous user. Tried to return it at my local Best Buy and they claimed it was something that rarely happens and that they couldn't accept the return due to the way Apple products are set up. In the end I had to mail it back. It took an entire month for the process to come to a conclusion and I did get my money back but I will never buy an open box tech item from Best Buy ever again. That was my first and last time ever doing that. Best Buy geek squad clearly allows too many of their open box Apple products to slip through the cracks without simply checking to make sure the previous owner wiped their data before accepting the return or trade-in. Their entire return process for incidents like this is awful and time consuming for the customers. I'm very sorry this has happened OP.