Heartbreaking yes, but some good has come of this. The myth that a dog needs to have a litter before being spayed has been broken in the eyes of these people. And they will be a help in spreading the word slowly whenever they hear somebody talking about having that first litter. Their experience can help prevent other people from going through the same thing. And maybe this dumb vet that told them to have a litter will open his/her eyes (though he is making money off this little scam).
In the US we have a website that we can use to rate vets and comment on them so people can find a good vet. Maybe you have something similar?