I hadn't even seen the give away you were doing, but I'm so sorry this happened. Some people are just greedy idiots and can only fake their happiness by tearing other people down. I wish I could say I'm surprised, but I've experienced the same thing in life and in WoW. I used to do Hide n Seek games for gold in SW or IF and people would try to scam me or throw a shit fit if someone else beat them to the prize. After the final time where a group of people attempted to scam me I haven't repeated it.
I will say this much, I love what you're doing giving away pets. I'm sure it means the world to people who are starting their collection or have had crappy luck on a drop. In some cases just bothering to show some kindness can brighten a persons day when they might need it the most. If you do decide that what you're doing is worth it (and I firmly believe it is) I would like to contribute some pets of my own to your store.
Screw the haters, you've made at least one fan today.