The API returns a simple result: score. The score is defined as value between 0 and 1, where 0 means no-spam-mam and 1 stands for damn-obvious-spam. Everything in between should be handled on your side.
Some words about how we deal with scores in our application:

• Typically - based on our experience – a really high probability starts at 0.75.
• Everything below 0.25 usually is fine.
• A score between 0.25 and 0.75 can be called risky and additional tests or analyzes should be done.