Morally you have to decide what is right and what is wrong. If it's wrong to decieve someone even though you've been decieved yourself, then you should notify them and offer to refund the purchase price. If you feel no responsibility for passing along getting lied to, then there is no moral wrongness and life goes on.
Now ethically, that's another matter completely. Ethically you should notify them and see if they want to work something out or just let things stand. But ethically to be silent would be morally wrong because ethically you need to speak up about wrongs.
Call me a bad breeder, Because I dont know how to contact half the people I've sold to.. Only the ones that keep in touch..