I can assist with your concern so that your VAT will be calculated accurately in QuickBooks, Juan.

The VAT calculation would depend on the tax code. If the commission service item you've entered (-30,000) is taxable, only the tax under the R270,000 amount will be visible on your tax reports.

Since you need to calculate your VAT for the whole R300,000 amount, we'll have to mark the -30,000 item as tax-exempt. This way, you'll have an accurate tax calculation. 

We can achieve this by following the steps below:

1. Open your QuickBooks account and select your client's name to access their company file.
2. Go to the Sales menu and select All sales.
3. Look for the transaction you've created for the sale and commission. Then, click View/Edit.
4. On the commission's item line (-30,000), select Exempt under the VAT dropdown.
5. You'll then notice that on the VAT percentage, the overall total of R300,000 will be taxable.
6. Once done, click Save.

After that, you can run your Tax reports and notice that you now have the accurate tax calculation for the R300,000 sale.

Additionally, there are several reports that you can maximize to track your sales and inventory status in QuickBooks. It lays down information about the items you buy and sell depending on what data you want to review.

Keep me posted by leaving a comment below should you have more questions about your VAT in QuickBooks. I'll make sure to provide prompt assistance.