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. This is typically achieved by first attaching to the meta 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.