Yeah, I think that's worth a try if something similar happens to you. I like company who can be flexible.
Here's the mail I received (no mention of "goodwill")
Thanks for writing to us about the recent price change on "Get Lucky (Deluxe Boxset: 2CD, 2DVD & Vinyl) [CD+DVD]". I recognise you have a choice of retailers and appreciate that you prefer to order from us. Please note that we do not extend a post-order price guarantee.
I've reviewed your order and see that the price change was significant and you just received this item from us. Under the circumstances, I'll make a one-time exception for you and issue a refund for the price difference in the amount of 8.76 GBP. Refunds usually go through within 2 to 3 business days and you will see this amount credited on your next statement.
(....)
Please understand that I'm issuing this refund because of the exceptional circumstances, and I'm doing this for you against our standard policy.
****WHY DON'T YOU HAVE A PRICE GUARANTEE?****
While we don't always beat the best available price on every product, we do offer deep discounts on many thousands of items. From time to time, prices on some items will change due to special offers from suppliers and manufacturers or our inventory and sales volumes. When we can offer a lower price for new purchases we will, but we cannot extend these discounts to completed orders.
Please accept my apologies for any inconvenience caused.
Thank you for your patience and understanding.