"Sounds like normal personalization of Google serps."
Its not. And if a select Dallas in the left of google, or spoof being in dallas byt setting my ip, i get totally different results.
Spoofing being in dallas, i get the real dallas results, where the client's website is at 19.
Setting Dallas as my location, I get the same results as if i don't spoof a dallas IP, except there are some google places listings showing.
My client's website, ranks at 156 when the user is outside the US, 25+ when outside dallas, 19 when inside dallas.
Competitor sites change up and down by between 3-10 places, this site by over 120 places.
This is not a normal local variation.
But its fine, its seems my answer is "No, no one has ever seen it before."