Westfield Facebook Competition Doubles Page Likes

Westfield recently ran a competition on their Facebook page to give away $10,000 worth of shopping vouchers. What caught my eye was it's spin on the regular giveaway format. The "Show us the likes, we'll show you the money" competition was pretty self-explanatory. Every new like added $1 to the prize pool and entered the visitor to win the total amount. The normal concept of a competition actually discourages organic sharing - afterall you want to win - the less people entered the greater your personal chance. In this case, the more of your friends that enter the greater the prize value.

Enviable Elements
The current number of likes appeared in the clothing so you could see what you could win, no cap was mentioned so their was a feeling that this go keep rising. Unfortunately the competition just closed at 10,000 likes. When I first saw this yesterday the page had around 5k likes - so they have at least doubled their previous likes very quickly through this promotion.

The competition is really simple - no entry form to be completed - just click "like". This did make me wonder though, even though this is housed on an app does the "like to enter" model breach Facebook's compeititon rules? [Update: unfortunately yes this model does break Facebook's competition rules]  

So what do you think - is $1 a good price for a "like"?
A quick look at online information available estimates the cost of one like from $1 (The Next Web) up to $3.50 (Panorama) meaning this actually might be a cost effective approach - but will this engagement last past this giveaway?