Typically, if you buy a home at trustee auction, you're accepting all the liabilities associated with the property, including any back taxes, permit issues, or any title issues. That's why auctions tend to offer discounts against retail market price as it rewards knowledgable buyers for doing their homework. If you worked with a Realtor, you can get some help to determine your options.
Hi. Traditionally, the back taxes should be paid from the seller's proceeds at closing with the current tax period prorated by the number of days the buyers owns the property including the day of closing. The seller is responsible for any liens including contractor's, HOA, etc. If the property was bought at a tax sale, you bought a tax lien agaisnt the property that covers the back taxes.