I also think selling your own daughter is the worst. Compared to the wife or the sister, the daughter is younger, less experienced, less powerful and somehow she depends on her father, even if she is of age. Therefore victimizing her is really cruel. And this happens every other day in RL.
It may depend on context of what "offering off" means and the build of the specific world at large. Giving daughter up for marriage with interest wasn't all that uncommon in certain circles not that long ago. Then, barring a father, taking authority over sister may be likewise expected.
But if we talk about expected contemporary cultural contexts, hinting that sister might be available for certain attention may probably be less creepy than outright prostituting a daughter.
Then, if we talk about wife & daughter combo deal, that might have a special appeal just two random girls (wife & sister) may lack, for profitable creep factor and more.