So, I would presume that it's important to keep contest giveaways small enough so that they look believable. I think I would suspect something as expensive as a $10,000 prize as well and, in fact, do suspect that the FB ads, which offer big-ticket items for free, are scams. I'm sure you've seen them: free iPads, computers, and "you are our 1,000,000 visitor", etc.
I do like your avalanche analogy. Made me smile.