Okay, let me clarify a few things regarding the slave-master relationship here.
Firstly, the slaves you're able to purchase or acquire in MoR right now are untrained girls who definitely didn’t see themselves ending up in a crumbling, old house together with a sadistic master. They are captured brigands, non-sexual maid servants, educated merchants/academy applicants, or high-willpower criminals that'll take shit from no one (except Amelia/Piper, who are almost, but not entirely, docile). They'll offer the MC a tough time, screaming and cursing at him for weeks if he decides to go the not-so-kindly path of molding them into servitude.
Compliant slaves will see the day in Crystal Hills, once that goes live. And they'll cost more than just the small-cash you throw at the Kymanto slave handler when buying one of the currently six available captives.
Secondly, if a slave refuses to scrub you in the shower, or lay with you in bed, or give you a blowjob, there are many ways to correct her already, even if those systems will be heavily expanded in the 0.8.X line of updates.
You can scold her – explain sexual/domestic chores in a dominant way, scream at her with lewd sexual suggestions, or talk dominantly in other ways offered through the interaction system. You can also use aggressive petting during seduction and use dominant "dirty talk" to affect her. All this will probably make a fiery girl angry, but it'll also have a chance to slowly disintegrate her willpower.
And of course, if this isn't enough, or if you want to show her that she's just a pleasure hole, buy a rope and tie her up. That'll leave her body completely at your mercy (Bondage section).
Actions like these always have a chance to instantly lower her WILLPOWER, based on if a skill roll is successful or not, OR, in some circumstances, pure chance.
You should also keep track of a slave's Humiliation value while forming her with the dominant approach. If this has reached 15/15 before going to bed, her WILLPOWER will automatically decrease.
Tie the girl up during nighttime (through the bondage section) or increase your security measures to keep her from running away. (I'll add a prison chamber and make slaves less keen on escaping if you have active mercenaries in your troop in a future update.)
But lastly, I acknowledge that there's a need to expand and refine these systems to make them more realistic. I'll dive deeper into this after expanding Westside slums, which is next up after the Inventory/clothes revamp that'll go live next weekend.