All of this advice is 100% wrong.

I also am a QBO accountant and have the same problem. First, there is NO option to delete a client. And setting them to inactive does NOT hide them. They're still in the list showing as "inactive." I have contacted support about this for TWO YEARS. They keep promising to fix it, then don't. Every time I contact support it's like starting over because the next Intuit rep has NO idea what's going on. They say they have to "research it," then I never hear from them again. The online support is a joke and horrible.