I ran into this when I tried the game out some time back. Didn't know what to do so I picked up guild contract. The problem was RNG decided those were all for D+ or C+ Gladiatrixes. And the stat/skill requirements make the base rank requirement a farce.
This would be a good place for some balance changes imho. If the titles/professions are supposed to be that hard to achieve maybe only ask for them with rank B or higher. Or have them only show up once your guild rank or brand is at a certain level.
All you need to achieve to get a slave a certain "title" is a skill mastery corresponding to B+... you shouldn't try to start with Gladiatrix Slaves if you have no combat skills yourself.
If you play as the perverted kid (hard mode) I suggest you start with "artist" slaves, 1 Male dess to level artisan skill to level 1 than train 3 skills of the slave to level artisan level to 2, again to hit level 3 (B+)... congratulation you completed an artisan slave, change atire and train her in another or more skills (again use corresponding male dress to unlock levle 1 training) in order to prepare yourself for a greater variety of slaves.
And personally I start with guild contracts as early as I can... in hardmode I suggest selling artist slaves to the "Anatomical Theater" in House Necropolise district until you can train atleast artist, servant and assistant slaves (Educator B+, Steward B+ and Artist B+), avoid Gladiatrix and Witch Doctors until later.
You don't want to make your slave a better fighter than yourself, and you need a laboratory to increase Alchemy skill (+20 Sparks on the the bill)
Also save up 10k $ and move to any district (I suggest Camilla/Beastmen at the start, as they are the cheapest in rent) and than try to train the slaves for the "special buyers" in the Forum in White Town to unlock those incredible powerfull items