Sorry I have taken some time to update you, it has taken me many tests to see if the lens is ok.
I think the focus mechanism is acceptable but it is not very smooth compared to by mother Nikon lenses.
I am not sure if this is normal for the lens or not as I have not used this lens before. If it is not normal for the lens and should be smoother then the $50 refund is fair. If it is normal then a refund is not necessary. What is your opinion?