Hello, Homer,
Matthew 19:16-17 (New King James Version)
16 Now behold, one came and said to Him, “Good Teacher, what good thing shall I do that I may have eternal life?”
17 So He said to him, “Why do you call Me good? No one is good but One, that is, God. But if you want to enter into life, keep the commandments.”
Here we find a man, who thought Jesus to be merely a man, referring to Jesus as "good". Jesus informs the man emphatically that no one is good but God.
We may compare, however, the textual variant, followed by the NASB, NIV, etc.:

first of all, the man does not call Jesus "
Good teacher," but simply "
Teacher";

second, Jesus responds with "
Why are you asking me about the good? One is the good."
So we have here some contradictory evidence. Mark, Luke, and some manuscript evidence for Matthew focus on Jesus and render the exchange in the sense that "
no one is good but God"; other evidence focuses on the man's question and renders in a rather vague line - that one thing or person is good.
Which is more trustworthy? We may entertain a number of considerations:

On the one hand, it would be understandable if the "vague-line" reading of Matthew were to have replaced a pattern like that of Mark and Luke in some manuscripts, if certain scribes preferred to deflect the propostion that "
no one is good but God";

On the other hand, it would be understandable if the "vague-line" reading of Matthew were replaced in some manuscripts by certain scribes, in order to bring the text into agreement with the pattern in Mark and in Luke
(this kind of editorial adjustment is not unknown in the body of manuscript evidence);

Then again, we may hypothesize an original comment that could have been vague enough to spawn
both kinds of "fleshing-out" in the manuscript evidence. If Jesus' response were something like:
Why "good"? One is "good" - then each of the variants could have nuanced their version in an attempt to more clearly communicate the meaning they perceived.
But such a terse response could be construed in still another way, especially if the tone were ambiguous
(or simply unavailable to a secondary witness):
"Why [are you asking about a] "good" [thing]? [Only] one [thing] is "good"? But if you want to enter life, keep the commandments [(as in plural, mister - stop trying to low-ball it)].
Shlamaa,
Emmet