Labor Laws - Commissions

[MasterLJ]

I'm not sure if this is the best place, but since I assume there are several business owners who post here, maybe some kind soul could help.

I've read a lot of CA Labor Code, and it seems sketchy on the details of commissions. It seems to defer to the contract signed between sales rep and employer which sounds like the employer has carte blanche to change it with the threat of dismissal if the sales rep does not wish to conform to the changes.

My most pressing questions relate to overhead calculations:

1. Are there any items specifically forbidden to be charged to the sales rep? (payroll taxes, health insurance, etc)

2. Can an employer legally retroactively charge for overhead adjustments? (e.g. They make a change to overhead in December, and want it retroactively taken out starting from the previous June... this obviously means a ridiculous hit to your commissions)

3. Not related to overhead - How difficult/easy is it to prove in a Court of Law that an employer mislead an employee from one position to their current position? I've read up a lot on the laws for this and it seems extremely cut and dry that any sort of misleading on the part of the employer is a misdemeanor and punishable by a fine to the state as well as double compensation for the employee.

Thanks in advance!