Client specific prices Is it possible to have client specifik prices for products in Commerce? 
This should be an option with specific clients that has an agreement with the company. Everyone else will pay the ordinary prices.
Yes, it's possible. I would recommend using role based pricing. Customers who deserve the special pricing should be given a specific user role. Then on the product type, add a secondary price field used specifically for users with that role. Finally, add a product pricing rule that checks to see if the order owner (i.e. commerce-line-item:order:owner) has the user role. If so, you should swap in the price value from the secondary field using "Set the unit price to some amount" and fetching the secondary price using the appropriate token. Remember that you'll have to first run an "Entity has field" condition on the line item to find its product reference field and again on the product to find its secondary price field.