The arts of phantom potion making were complex, and demanded a specific skill set dedicated to them. Timothy realized that as soon as he entered a chemistry workshop!
Now, this line of work wasn't shunned upon, entities practiced it openly, and those who did practice it, were either really powerful or really wealthy, so they had nothing to hide. One could set up such a business in the ghost world, and if they were skillful enough, they could become really wealthy! Although the currency here was useless in the physical world, it was still the standard currency of trade here in the city, and across the entire Kingdom of Mors Florentes, meaning that hundreds of thousands of ghosts used this currency! It was a good place to be skillful.