Like eBay?
I bought a tablet on eBay last year. It was defective, but the guy replaced it at no cost to me. The replacement was also defective, so I sent it back and got a full refund. I got another tablet from another seller and it works perfectly.
It's tricky. Most people that sell them don't know anything about laptops.
Make sure to read their return policy as well. Some won't accept returns.
Your first time purchasing did you request a new one or an old one? Was it a defective brand new laptop.