The only way you can know for sure is to get an inspector that has come highly recommended. I've been on hundreds of inspections and most inspectors certified by ASHI will have had training and certifications to at least be called inspectors. After that though, I've seen a range of people with varying knowledge, skills and experience. The inspector I suggest I've been using for over 13 years. They know what they know and they know their limitations and will call for further technical inspections when required. A home inspector is a Generalist, not an expert in every single facet of a home.
You can review some sample reports to see how easy and clear they are as well as how comprehensive. You can ask what technology they use, my favorite inspector uses infrared scanning cameras to literally see through walls, detecting temperature variances. This has caught leaks and issues that other inspectors would have missed.
Ask your agent for two or three suggested inspectors and check out their websites.