I can't claim an immigration officer never stamped my passport, but I can claim that a wrong date was stamped.
My wife had booked my flight from the U.S. and had me leaving 28 days after arrival in Thailand. On departure, immigration told me that I was 3 days overstay. They would only go by the date stamped in my passport. When I gave the officer the ticket showing when I arrived in Thailand the officer looked at it briefly, gave the ticket back, and then told me, 3 day overstay 1500 baht!
P. O.'ed, my wife when she found out and she called to complain to her cousin (an immigration officer) after I returned to the U.S. but he said it was too late to do anything about it.
As an aside, I miss the good old days, when my wife had relatives working in immigration, before fast lanes. One of her relatives would meet me as I deplaned and walked me through to the diplomatic immigration process area. Strangely enough, the first time that was done, the diplomatic process area was through a door, into a short hallway that led to a stairway up to the baggage claim area. I think that was shortly after Suvanabhumi Airport was built. There were no signs on the door. I guess you had to know which one to go to.