One of the basic differences between a service panel and a sub-panel is that at the sub-panel, the neutral bus bar floats. This means that the bus bar is electrically insulated from the metal cabinet and the grounding bus bar. This is typically achieved by first attaching to the metal cabinet a mounting plate of plastic or some other non-conductive material to which is the neutral bus bar is then attached attached.

The degree to which a bonded neutral in a sub-panel is dangerous depends on who you ask. It's recommended that you not state the degree to which a bonded neutral is serious unless you feel that you can explain your reasoning clearly and logically in court. It's best just to state that it is improper, recommend correction by a qualified electrical contractor, and move on.