Q: Problem with iPhone 6 plus Touch ID

So I bought an iPhone 6 plus from a store that sells phone and I am pretty sure that the phone is used. Well the problem is that the touch id for the iPhone 6 plus is really hard to set up and it only works with the tip of my fingers. I try to set up the touch id how it is normally set up but it doesn't work for me it asks me to use a different finger. I was just wondering if it was a hardware problem or just something else. Thanks for responses.