I think you should take it back to the guy who you got it from. I wouldn't really say it's a trusted seller. He was buying and reselling by jacking up the price by couple of hundred bucks. In fact it took him a while to sell this one cuz he got called out many times. You should have done you research first..
Anyways, I had this watch form Burnz and it was working like new when I had it. I'm not sure what the previous owner did but if I were you I should ask him what happened or send it back and get your refund.