Debating whether to purchase 2007 Mazda 6

Hello! I am debating whether to buy a 2007 Mazda 6. It has 77,000 miles, automatic, and a rebuilt title (hit on side, had to get door replaced). I took it to a garage to have it looked at and he said the transmission is jumping from 3 to 4. Also, the transmission fluid is black, he recommended getting it flush and changing the filter. The owner is doing this, thinking it might fix the "jump" from 3-4. Any thoughts about this purchase would be greatly appreciated! Kind of scary about the black fluid and the transmission problem but I am wondering if this is an easy fix or a horrible sign of something about to go wrong??
 
Wrong section man. I don't personally think ATX fluid should be black, but I'm not an expert on ATX's by any means. Make sure he gets the fluid FLUSHED and the filter changed, not just a drain and fill as a majority of fluid is in the torque converter and won't come out with a drain and fill. Is that a 6-speed ATX in the 07? Transmission repairs are not cheap so if you have any doubts, I say stay away, maybe get a second opinion from and other mechanic as well.
 
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