It’s a complex subject. The word mercy and the word merchant come from the same root. Mercy definitely works hand in hand with the blood purchase of the sinner, which means God has set that sinner up for a guaranteed repentance (i.e. an ultimately completely successful restoration in thought and in action to alignment with God’s desirous will). (Unabashed crazy-evangelical bible theology here.)
And yet we can speak in another sense of having mercy on an unbeliever and not be talking utter nonsense. One could also have mercy on something like a horse or a dog.
Shades of C. S. Lewis distinction making???
Not so much...particularly if you look at the original languages of the Scriptures. In Greek, mercy is ἔλεος (eleos), while merchant is ἔμπορος (émporos). Two completely different words.
Even in the English, the etymology of the words is not the same: they both have Latin roots. Mercy is derived from the Latin misereri (to have pity or compassion on), while merchant is derived from the Latin mercari ("to trade, traffic, deal in").
That is not to say that we aren't redeemed by the precious blood of the Lamb of God (1Pe 1:18-19), but the two words are not at all related.