Ok, I have a bit of an issue going on. I am doing contract commission only sales. I am selling advertising and getting paid 25% of all sales. Quite a few of my big accounts recently had their advertising contracts become effective for billing on Jan. 1. I would like to get paid on these, but the employer will not pay until they have sent in checks. If I were to quit this employer...would he still have to pay me on those contracts even though the customer has not paid?

Not necessarily. It depends on the terms of the plan as to when commissions are "earned". It is not uncommon nor illegal for plans to provide that commissions are not earned until the customer has paid.