Needing a sponsor
I'm afraid it's not good news mate. To qualify for sponsorship you will need to have an occupation on one of Australia's Skilled Occupations Lists.
An update to the list is expected in March however sales assistant is not one of the occupations that has been flagged to be added.
Does your wife work and does she have an occupation listed?
Alternatively, if you are young, retraining could be an option?
All the best
Getting Down Under