Egg - Giving away 'up to' £12,500 per month for 3 months.

Egg are using weasel words to make a promotion sound better than it would, at first glance, appear.

A "reminder email" [1] informs me that:

We're giving away £50 to up to 250 lucky Egg Money customers each month. Customers who pay for something with Egg Money could be in with a chance of winning £50. And that's on purchases of all sizes – big or small. Conditions apply.

 Hmm. "Up to 250."

0 is included in that amount. They wouldn't, would they? Lets have a look at the conditions they link to:

1. When you make any retail purchase between 12 November 2009 and 31 January 2010 with Egg Money, you will automatically gain an entry into the promotion. Winner(s) will be selected on a monthly basis; transactions made during a calendar month and posted to accounts within 5 days following the end of each month will be eligible for entry in that month.

Did they really need to put the plural-s in parenthesis? That would appear to indicate that they're allowing for the possibility that could be only one winner in a month.

So how are they actually generating the winners? Well it's random. In a way that it is indeed possible, but unlikely, that there could be no winners in any one month:

7. The winner of the promotion will be an Egg Money cardholder whose last 4 digits of their 16-digit Egg Money card number match sequentially with the last 4 digits of the 6-digit sales authorisation code shown on the sales receipt following a completed merchant transaction.

So, each transaction has an authorisation number assigned to the merchant by Egg. If the last 4 digits of that code match the last 4 digits on your credit card, "You've Won!!!" Other conditions prevent you winning more than once a month.

What are the odds of you winning, provided 250 other lucky, lucky people haven't yet already?

I reckon it's 1 in 10*10*10*10, so 1 in 10,000, presuming both authorisation codes and the last 4 digits of the card are suitably random, and not skewed in any fashion.[2]

So, if you, personally, make 10,000 purchases you might be in with a good chance of being £50 better off.

That's 123.5 (roughly) purchases per day, every day, for the duration of the promotion, provided you started buying on 12 Nov 09. Relevant tidbit: Egg are notoriously stingy with their limits on this particular card (or they used to be before they re-branded it and started charging new customers £1 a month for the privilege of it bulking out your wallet/purse.)

Something that caught my eye towards the end of the T&C's (and I'm including part of clause 1 again..)

1. When you make any retail purchase between 12 November 2009 and 31 January 2010 with Egg Money, you will automatically gain an entry into the promotion.

15. The winner(s) agree to take part in reasonable publicity.

17. Participation in this promotion constitutes acceptance of these terms and conditions, including any decisions which The Promoter may take in order to safeguard a smooth proceeding of the promotion.

I can't find any way to not end up being enrolled in more advertising against my wishes - i.e. opt out of the promotion, except by not using the card.

Is this entirely reasonable?

[1] i.e. spam I didn't ask for, I'm usually most meticulous about un/checking boxes as required to only obtain necessary communications. Telling me my statement is ready, and may be viewed online I consider 'necessary,' sending me repeat emails encouraging me to use my card are not.

[2] Well credit card numbers (when considering the number as a whole, and not just any part of it) are not random. The first few digits are an Issuer Identification number and the last digit is the Luhn Number (a check sum,) making at least part of the number dependent on the rest of it.