Oh. I forgot to add, check for vibrations and foam in the tank when U ask the bloke for a test flight. Listern to the motor, if you it should have a constant sound if not ASK.( the motor part comes with experience so this is where a experienced flier would be handy)

Vibrations / Foam = Bent or out of track items.(Easy way to check if keep an eye on the tail fin when the pilot hovers it)
Ask the pilot to "punch" the stick and check the climbout of the heli, it should climb quickly( a bit slower on a 30 )
Check the frame for cracks/broken pieces and any damages.

let met know if u get something, worth while.

cheer
l0n3i200n