The checkout dive was requested by the diver....The inability to set up gear rang alarm bells but not really loud.
In which case, you fulfill their request by providing honest feedback after the check-out.
However, in doing the check-out you now put yourself in a position of liability because you cannot deny foreknowledge of the divers' competency level. This knowledge has to shape your risk assessment regarding what diving activities you are prepared to take the diver on.
If the diver does not display competency, as determined by the
appropriate certification performance standards for the dives undertaken, then you are failing to apply reasonable and prudent risk management.
As a baseline, any diver should be competent in
all of the performance standard skills taught on entry-level diving. Being incompetent in OW level skills signals a hazard to safe diving and a risk to the diver and those around them. This has to be rectified.
If the dives being considered are beyond OW level, then additional training performance standards need to be considered in respect to diver competency. Either way, the diver has to be
actively and
currently competent at the level to which they are certified, in order to complete dives at that level.
There is also the issue of regional suitability. Divers are qualified up to the limits of their training and experience. It's your responsibility to determine if that training and experience is sufficient for the diving you can take them on. If anything happens to that diver, then you have to justify or defend that
risk assessment.
I don't believe it is satisfactory to turn a blind-eye to diver incompetence and simply abandon proper risk assessment/management because the diver has X, Y or Z certification cards. That's a "see-no-evil", head-in-the-sand type of strategy... and if you've done a check-out dive with them, then you can't claim subsequently to not know that the diver was incompetent below the standards of their certification level.