Its quite hard remarking(without being obvious) when the Multiplyer is locked at a certain speed. Even if you unlock the "L1s" the default would be the multiplyer for the original CPU speed.
For example:
Thunderbird 1Ghz CPU has a default multiplyer of 10x, if you were to unlock with the L1s, in the BIOS you can change the multiplyer to 12, however if you were to choose "default clock", it would be changed back to 10 and would run only 10 unless you use a custom setting.
However, if they used Tom's hardware guide and did the L1s to the multiplyer settings, then you would have to physically look at the L1s and see if they have any tampering. It would take quite a bit of work to make it look "authentic", and quite a bit of L1 breaking and connecting.