The commonsense interpretation of Jesus' reaction to the address "Good teacher" is that Jesus distinguishes Himself from God and denied that He is good: "Why do you call me good. No one is good but God alone (Mark 10L17-18)." Notice how Matthew, in copying Mark, recognizes this and takes so much offense at Jesus' response that he replaces "Good teacher" with "Teacher" and totally changes Jesus' response in Mark with "Why do you ask me about what is good (Matthew 19:16-17)?" The only way to avoid this scandal in Mark is to assume that Jesus is trying to elicit a recognition that Jesus is both "God" and "good" from the rich young ruler. But 2 points rule this option out:
(1) Nowhere in the context is Jesus' identity and true nature mentioned.
(2) Jesus calls Himself "the Son of God," but never "God." Notice how Jesus' denial of personal goodness fits neatly with His felt need to receive John's baptism of repentance. This need is not explained away by John's protest in Matthew 3:14-15.
So what's the explanation for Jesus' shocking question in Mark 10:18?
(1) By "God" Jesus means "God the Father" and so He is distinguishes Himself from His Father.
(2) The Father is the source of all goodness, and so, Jesus is sinless in the sense that He too derives His goodness from the Father and in the sense that Jesus did nothing to separate Himself from God, even though, being fully human, He had to learn by trial and error just like any humanl