hard to prove what? you're assumed guilty
Anyway I've had stuff from hobbyking and you can choose what value they declare it as
had a 130$ package declared at 70$ value and it was inspected by customs with a customs sticker on the side.
They never said anything, I guess they are more bothered about stopping drugs than someone falsely declaring a parcel to an individual.
I'd imagine if you had a container of XXX and declared it as XXX to save on import duty they would nail your balls to the wall though