Good day 

Please refer to your employment contract, the contract should state the type of commission structure you will be using. The contract should also set out the negotiated deductions these include running costs(if any) as well as Point of sales transactions/fees. These deductions have to be negotiated between the employee and employer as it will naturally come up depending on the salary structure. The employer has to deduct PAYE as well as UIF other deductions are situational such as damage/loss. 

Depending on the industry it has become common practice for an employer to deduct POS and speed point transactions from the employees tips/commission. 

The employer has to at least make the employee aware of these deductions. 

Regards LP