Sounds like you might have bought a relatively new property where the property taxes had not yet been assessed. If that's the case your agent should have included a clause providing for a reasonable hold-back to cover the potential tax liability. However, even if such a provision was not included, the standard Agreement of Puchase and Sale includes language which would require the Seller to re-adjust to cover the unpaid taxes for the period of time that he/she owned the property - collecting from them, however, is an entirely different story. Best bet is to speak with your lawyer about the matter ASAP. Good Luck.