There's no silver bullet
Map-making for “good” copies of maps is really a matter of redrawing them from scratch (digitally or physically), using the original design as a reference. There's no easy or automated way to transform a hand-drawn map into a “good” digital version.
Cartography (digital or analogue) is both an art and a technical skill, and like all arts and technical skills it is only achieved through years of practice.
Unfortunately, this means that there are only two ways to go from hand-drawn to publishing-quality:
- Develop one's own art and skill until it's at the desired level.
- Hire someone else's years of artistic and technical development.
Then the cartography artist redraws the map as something professional-looking.
A few years ago I had been practicing, for about a year, a particular style of finished-quality cartography inspired by Dyson Logos's professional work. The result is the map published in The Tomb of Nesta the Mischievous, a One-Page Dungeon Contest award-winner that can now be found in PDF on various sites and in the printed One Page Dungeon Contest 2012 Compendium.
That's what's possible with approximately a year of about an hour of practice about every day or two. (Mileage may vary of course, depending on existing skill levels and dedication!) If that's an acceptable investment, timeline, and outcome, then that's a route you could take.
Otherwise, a professional publisher is best served by hiring a professional cartographer that specialises in RPG maps, because maps can really make or break their adventure.