You may be able to sue on one or both of the following theories:1) Breach of contract: when one buys a car, one is usually considered to be paying for an unemcumbered vehicle with clear title (so no back taxes) and which is legal to drive (i.e. passed emissions tests). Failure to provide such could be considered a breach of contract.2) Fraud--it is often considered fraud to omit to disclose information that any reasonable buyer would assume the seller would disclose, such as that a car is not presently legal to drive on the streets (emissions) and is encumbered (taxes).  It is also certainly  fraud to affirmatively lie about these things. Thus, the seller may have committed fraud.Other fraud or breach of contract could provide a basis for recovering compensation.