Hmmm when an author says they've gone through multiple illustrators, that's a huge red flag for me. One - okay, understandable, benefit of the doubt situation. But when there's multiple that didn't work out, that leads me to believe the common denominator is perhaps this author is hard to work with.
I'd suggest still doing the meeting with him, but asking all the questions you can beforehand. And if you do decide to go ahead, make sure to have a contract in place that includes how many revisions/additional fees if the scope becomes bloated, etc.
Then you just have to decide how much 'art direction' you're willing to take from him or how you'll go about educating/putting your foot down otherwise.
Best of luck! Let us know how it goes.