Never buy a floor model

I bought the floor model top mattress in the store I layed on it, it felt good, once I got it home one side of it was lower than the other side where people sat on it, I didn't fill all of that when the salesman put it on the floor, I paid 400 dollars for the same mattress I threw out that I had for ten years. Still need a new mattress set, not happy with this one at all.