If you suspect your boss is stealing your commission, begin by gathering evidence, like emails or sales records. Confront your boss calmly and professionally, expressing your concerns. If the issue persists, escalate it to your HR department, presenting your collected evidence. For substantial sums, seeking legal advice could be beneficial, as this constitutes wage theft. Remember, it's essential to work in a fair and respectful environment. If these steps don't resolve the issue, consider finding new employment where your contributions are recognized and appropriately rewarded.