Every charter company has their own standards to qualify prospective charterers. Some may accept the ISSA Inshore Skipper certification alone but most will also ask for resumes of experience. The ISSA Inshore Skipper certification will show the charter company that you have received formal training and have passed a rigorous program with specific standards.
Charter companies look at a variety of variables in qualifying a charterer: experience, certifications, size of boat being applied for, charter area and conditions, and the experience and certifications of crew members.