With regard to tone arm bearing wear this is most often tone arm bearing damage, not wear. Badly transported, badly handled or sometimes over tightening. Some arms use the arm pillar as races for the bearings (some linn models for eg) and over tightening the VGA arm collar can distort them.
Sometimes it is just crud and goop that can be hard to get out or even corrosion.
Care should be taken when mounting, fitting, packing or moving an arm.