Is it permissible to agree with the employer on a variable commission (2% after 70,0 SAR and 1% before it) on sales?

It is permissible to agree with a worker on a varying commission based on the volume of sales. This falls under the category of ju'alah (reward for a specific task). The condition is that the ju'l (commission) must be known, not unknown, and that this ambiguity does not lead to withholding delivery or disputes. This oscillation between two states does not cause harm as long as it ultimately leads to knowledge with a known criterion.