IFRS hardly specify what sort of expenses should be recognized into cost of sales and what should not be taken into cost of sales. It only states the basis of recognizing costs. see that IAS 18.19 reads as follows "Revenue and expenses that relate to the same transaction or other event are recognized simultaneously; this process is commonly referred to as the matching of revenues and expenses"
Therefore it is up to the management to decide whether a particular expense fits into cost of sales or not. In your case you need to decide whether you should include the commissions inside cost of sales or in marketing expenses (outside of cost of sales). If your agent commissions are directly attributable to sales & the commission costs varies in line with sales, I dont think it is wrong to include it under cost of sales.