How do I know if the title of a real property is "clean" in the auction.

It is not uncommon for a purchaser at a foreclosure sale to find out after the fact that there are additional liens that are senior to the one foreclosed. Also, property taxes can be unpaid and there could be IRS tax liens that allow the government to redeem the property. If you are contemplating such a purchase, you should get a preliminary title report from either the trustee, who might send you a copy of the one it ordered, or from a title insurance company. You will want title insurance if you take title.