In the past year I've seen a half dozen home sales have their sales price be very different than the market value simply because the seller didn't know how big the home was. Its a simple process to hire an appraiser to measure your home and know for sure what you're selling.
In some cases, the county included the garage in the living area of the home, and as a result, the contract price was well above the market value, by approximately the difference in the value of the living area. Likewise, I've seen builder/flippers under report the living area of remodels because they simply trusted the tax record. In these cases 10's of thousands of dollars were left on the table.
When you unintentionally report the wrong living area, you not only will struggle to come to a right listing price, but the buyer pool that wants a home that is smaller/larger than what the home is reported as, may never see the home in their search OR will be disappointed when they arrive at the home and it looks different than all the homes they've looked at that reported the right living area. You're shooting your self in both feet - both the price and the buyer pool. Get your home measured, or at least, confirm the tax record you're going to report!