Tax values are never a good indication of value. Determined by computer...no one has ever looked at condition in most cases.
You want to look at comparable values....what has sold in your neighborhood that is similar to your home.
That's tough to do on your own. #1 you probably don't go in that many homes, #2it's tough to know how long they were on the market and what they actually sold for.
One idea is to pay for a certified appraiser to come to your home and give you a value. You can then give that to buyers as an independent source of value....should be around $400