One thing this trade is well know for is equipment that supplied with major faults that should never have reached the field. I will submit a couple that have given me grief, I'm sure we can build on this list

3 Phase (415v) package unit fitted with single phase (240v)compressor

Hermetic compressor with partially welded shell

250kg Reviever with dip tube welded in upside down

Evaporator coil full of epoxy coating