Pre-auction tax levy sale

[Shiyear Woodbury]

My question is if I want to buy a house to lower the chance of competition and I offer the person money and tell them I would also pay their back taxes in return for them to sign the deed over to me, what do I do or what happens if the house still has a mortgage? Do the payment roll over on me and I assume the payment (keep the mortgage in their name) or do the mortgage whip out and I become mortgage free? I'm confused so could anyone help me out thanks.