what does "sales disqualified" mean in local CAD?

[Benjamin Cowles]

So I'm picking out prospects from the local CAD based on my trips through the neighborhood looking for run-down, possibly vacant homes and just doing manual searches for properties with absentee owners with potentially higher equity based on last purchase date and comps. I'm in lee county btw. 

Often I find:

"Sales disqualified as a result of examination of the deed"

followed by either: 

"Disqualified (Doc Stamp .70 / SP less th $100 / Other Disq)"

or additional info indicating a transfer of deed where "no doc stamps were paid" usually with like a hundred dollars in place of the price, otherwise often I'll see a small price back around 20 years ago for under 20k, which I'll usually use for my records as the last sales price. 

So what is confusing is the often low price(not the often standard "$100.00", I figure is put in there as just a number required) despite it bearing the "sales disqualified" message. What does this indicate the situation probably is? Thanks