Somebody does not like Dumbledore or some of the Weasleys. HMMM. I enjoy the Dumblebash and the Ron bash. But given that Harry saved Ginny's life it would seem that, that debt would keep Ginny from being party to to such a fraud. If love potions are so easy than either people would by default be checking for them all the time as standard procedure. Ow that you bring up the black family and tonks I would have thought that the activity itself would have caused a judgement already on tonks.
Author's response
Actually I don't care for the female Weasleys, but like the males. The only reason for the Ron thing is to give Hermione something to escape from...
The life debt would keep Ginny from hurting Harry, as long as she can convince herself that he needs to be with her, she's ok.
Potions, easy to use, hard to make like the luck potion whose name escapes me.
The family judgements aren't automatic, they have to be decreed by the head of house.