If it is appraised at some amount, how would you know what is owed? Where would all these appraisals have come from, or are you meaning assessed tax values? The tax value has little to do with actual sales value of a property, but again how would you be able to guess what they owe?
The only way to determine approximately what someone owes is by noting the mortgage data in the tax record and doing an amortization on th eloan to get a rough idea of what their payoff may be. Only the owner knows for sure - they may have paid extra principal so it will be lower or they may be behind so it could be higher.