Thieves guilds usually have a network of informants. This helps them know about valuable targets, security details, etc. They also have to deal with rival guilds or other powerful entities in the city. In some novels, they may have a tenuous relationship with the local authorities. Sometimes they pay bribes to stay in business, and other times they are in direct conflict. In 'The Night Angel Trilogy', the thieves' underworld is constantly in flux as different powers vie for control.
It's likely about the adventures in the Sea of Thieves world. It might feature pirates, their quests for treasure, battles on the high seas, and the various strange and dangerous creatures that inhabit that world.
The top ten guilds with full-time experts could not be determined based on the search results provided.
While waiting for the anime, you can also click on the link below to read the classic original work of " Full-time Expert "!