One thing to be careful of--even with tax records--is they can be incomplete, inaccurate, or misleading.
Incomplete: The tax records may not show/reflect recent additions to a property.
Inaccurate: Sometimes the numbers (square footage, for instance) are just plain wrong. Or with my home, for example, the tax records show electric heat and say that gas isn't available. However, gas was run to our home more than 10 years ago, and we switched over more than a decade ago.
Misleading: The tax records might show that a property sold for $300,000. That technically might be correct. However, it won't reflect any "seller subsidies." So, for example, a $300,000 sale with a 3% seller subsidy actually netted the seller $291,000 (before other expenses). The real number you'd be interested in is $291,000, not $300,000.
A final note: Remember that what a home's last sales price was has almost no relationship to what its current price it. It can help with negotiating: If you see that the owners bought it 10 years ago for $150,000 and it's now on the market for $300,000, you know there's probably some negotiating room. But if they bought it in 2006 for $320,000 and it's now on the market for $300,000, it probably means they can't afford to go much lower. In neither case, though, can you tell what the house is worth today.
Hope that helps.