My mother is selling her 80 acres of farm land. She has owned it and rented it since the 1960s. It is my future inheritance. Is it better for tax purposes to add me or change the title over to me before the auction sale.

I'm confused. If this is your inheritance, why is she selling it? If you expect the proceeds of the sale to be your inheritance, then there is no reason to put you on the deed. And why is it going in an "auction sale".

To put you on the deed, she would have to sell, at least, a share of the property to you.

... Is it better for tax purposes to add me or change the title over to me before the auction sale.

The capital gains tax is at the same rate for either of you, so for tax purposed it doesn't matter.

But I too am puzzled by "auction sale". Is there something you aren't telling us?