I played a doubles match against a strong team a few years ago. My partner was playing great and we were up a set and a break with my partner serving. I watched one of our opponents (the other was fine) make 4 bad line calls in that one game to take the break back in the second. Twice he called serves wide from all the way across the court, that I knew for a fact were in since I was right in front of them.
My partner crumbled after that game and we lost the 2nd set and were bageled in the 3rd. We could have gotten a line judge after that game and it wouldn't have mattered, since the damage was done and so was my partner.