Be a native Japanese speaker. 
Seriously though, we did research on the names in the original book club, so many are listed in the original home thread.
If you look closely at the definitions in jisho, とめる and やめる indicate different kinds of “stopping”, so that’s usually a good hint. But as you said, とめる is also usually written as 止める, while やめる is usually written in kana. That seems to be the case in this book, as there’s a sequence (I think in this week’s reading, I’m not reading along to know for sure) which uses both 止める and やめる back to back.