The 7% commission arrangement would be between the agent and their employee. Your client wants to pay an incentive to a third party (i.e., the individual who sold the property)—this is not an employer/employee relationship.
Because the individual is not an employee of your client, this may be treated as a third party gift or incentive ‘payment’.
If there is an associate relationship between the vendor, real estate agent and employee then Fringe Benefits Tax may apply for a property fringe benefit, because the benefit is received as a consequence of employment. However, if there is no association between the entities, FBT would not apply.
If FBT applies, this could be significant on a $43,000 gift, so the vendor needs to know the full implications of the decision before he buys the car!
GST will be claimable if the gift is deemed to be tax deductible to the business. That is, if the property in question is owned by the business and not by an individual.
It will be the individual's responsibility to check the impact of this gift on their tax return with their own tax agent.
This is not a straight forward situation, and because FBT may be involved, it is highly recommended that you get tax agent advice and/or ATO advice.