Dead food is allowed to be sold on ebay because the animal is bred FOR food, so I doubt very much they will be taken off of Ebay.
My partner has all kinds of reptiles, snakes included. He buys frozen mice for his snakes (and the odd rat), as well as crickets and mealworms for his Gecko's, god knows how many breeds of frogs he has, and Preying Matus'. He has never fed his snakes GP's (and I hope once we move in together in a couple of months he never decides to feed them GP's...especially mine), as it is an uncommon source of food. If you think about snakes in the wild, they will eat GP's if they are avaliable and the right size for the snake (and sometimes even if not the right size). Everything deserves a shot at life, its all about the (and I know this sounds corny) "Circle Of Life".
The only snakes that will eat eggs, are egg eating snakes, it means they get the nutrience they need from the egg, so eating anything other will not benefit them much. The same as snakes that prey on birds. Most snakes can have a variety of things, mice, rats, birds, rabbits, and guineas (but how wide-spread are guineas in the wild?!).
Someone said earlier if this was a rat or mice board there would still be upset over it, its because it happens to be guineas pig (which is rare food for snakes) that its an issue here.
I personally don't like the thought of GP's being fed to them, but some people do it, I just have the comfort of knowing that its not a favourite on the list of food for snakes as it is quite rare food for them.