I'm not sure why you'd look at Zillow for estimated values. It may be entertaining, but it's not accurate. Kind of like the "Magic 8 Ball" you might have seen as a kid.
The primary item that determines value is what comparable properties sold for. Zillow is weak on that from the beginning, in that its computer algorithms aren't very good at identifying comps. The second problem, as Don Groff points out, is that Texas is a non-disclosure state. So if Zillow isn't accurate to begin with, then you put it in a state where it really CAN'T find comps, you're only wasting time with it.
Then, on top of all that, asking prices are just that--asking prices. Even if Zillow is 100% accurate even in a non-disclosure state, that doesn't mean that the asking price is on target.
Find a local Realtor who can determine what the property is worth. If it's worth more than other nearby properties, your Realtor will be able to explain why.
Hope that helps.