- Freehub body has abnormal marks (sprocket). Even with a cassette, you get one pronounced bit. Single speed is obvious. Cassette with alloy carrier and XC application - you get nothing, apart from one or two right at the outside of the splines... nothing like trials.
- Helical spolines - more wear than normal (alu driveshell mainly).
- Bearings, usually notchy, from being over tight. Often not bedded in due to not many miles.
- Axle ends usually marked in strange ways, from the axle slipping in the dropouts (when landing hard on bashring).
- Often damage to the left hand side of the hub shell.
- Abnormal wear on teeth of ring drive (more engaging-disengaging than an XC/DH hub).
- Scratched fun bolts (if it has them), with bits of brick/rock/blue paint in/on them.
I think thats it...