If there are not any other sources of data than the MLS and county tax records, you might try asking the county tax or appraisal dept. what information that they do not readily make available to the public on either their web site or GIS page. I work for the tax office in a relatively small county. We collect lots of data that is not available on the county website, however if asked, we will provide it if possible (It cannot violate privacy laws). Remember, this is public data anyway paid for by the taxpayer and subject to disclosure laws. You might be charged for the time it takes a county employee to assemble the requested data, but usually, a county will work with you if their CAMA software makes it relatively easy to export the data. Many times, what you think is the tax card for a property is really just an abstract of the actual card. Always ask for the actual tax card for a property if it is not available on the website because it usually contains a wealth of information if you know how to read them. Most counties also have timely very high resolution aerial photography from all 4 sides of every parcel in the county. It's how we find improvements that have not been disclosed by the property owner. This is usually not available on the GIS site except for the direct overhead view. Sometimes this aerial photography goes back for decades. Many counties will let you download the entire plat database from a link. They do this so that Google, state agencies, and other data users won't constantly bother them for it. You could request this yourself but you will need the correct software to view it. Look into getting ArcView. It's pretty expensive software, but it's amazing what you can do with it. Counties will NOT provide any income or expense data for a particular property due to privacy laws so don't bother asking. Many times they will provide confirmed sales data of commercial and residential properties (Sale price less any adjustments for personal property or other factors). Most counties send letters to the participants involved when a property sells. Ask if their confirmation codes are printed on the actual tax card and learn what those codes are. Many times, building permits along with the permit date, value, and what the permit is for is included on the tax card. You can use this to tell when a home was renovated or if other improvements were made after a sale. It also usually shows when the property was last physically inspected by the county and what type of inspection was made. Find out what improvements the county picks up and which ones actually effect value. Some counties don't pick up walkways or bulkheads for example, other do and put a dollar value to it. Most counties will post their appraisal guidelines or manual online which will show you how to read the actual tax card. Ask to get a copy. Be courteous and you might be surprised at how much usable information you can get.
