to intervene in this issue. Do a Jay and take pictures, take notes, don't pay anyone just yet, find all you can about fissures and cracks and pros and cons about marble and become very knowledgable yourself so that you can protect your investment and your integrity.
Does the installer have a boss? Contact him. Contact the manu of the marble and have him/her see the alleged defects.
Just freeze everything and dig in.
Most of the time, with good companies, the mission statement is: the customer is always right and will be satisfied. You need to remember this and go after your satisfaction.