While Samsung have been caught bumping GPU clock speed, it's not the only way to game the scores. Nvidia used to get caught regularly dropping in custom shaders, dropping precision and changing texture modes in benchmarks. Sometimes that had zero effect on render output and is actually an acceptable approach in non-benchmarking contexts, drivers usually have game specific hacks built in - nowadays with en\disable control.
Even GPU overclocking isn't always easy to detect, or likely to decrease battery life enough for certainty.
It's a repeat of the NVidia+ATI+others situation, with the same solution - repeated public exposure till they stop.