Amazon made a mistake; what to do??

[Faerie]

I ordered:
http://www.amazon.com/Retinol-Cream-...ywords=retinol

Pack of 3 for $17.

The amazon seller sent me 3 bottles of this stuff:
http://www.amazon.com/Original-Cellf...ords=cell+food

Which seems to be worth ~ $60-75. When it arrived I immediately opened one bottle up and used some (add 8 drops to a glass of water; drink). This was before I checked the prices, I was just so curious about it.

I checked prices after receiving this email:

Thank you for ordering Retinol Cream (Vitamin A Cream) 100,000 IU per ounce - 2 Oz (Pack of 3) through Amazon. We are the seller of this product and your order was fulfilled by Amazon.

We are very sorry to inform you that due to warehouse issue, you might have received wrong items (3 bottles of CELLFOOD) instead of Retinol Cream (Pack of 3). If you did receive wrong items, and still have them (3 bottles of CELLFOOD) in original seal, we'll be glad to provide you a prepaid return label for you to return it to us.

Once receive the return items, we'll be glad to mail you the correct items, plus 1 FREE bottle as our gift to appreciate your cooperation. That means you will receive total 4 bottles of Retinol Cream!

Again, we sincerely apologize for the mistake and all inconvenience caused to you. Thank you for your understanding.

Is it wrong to keep the more expensive stuff? My vegetarian diet often leaves me deficient in the way of certain micronutrients and trace minerals, and this stuff could really ++ my iron levels lol. Plus I'm poor, though I suppose that shouldn't influence the decision. I sort of feel guilty, but then it was their mistake right? And it's not like their store is going to tank because of one little mistake like this... but then it could contribute to increased prices for everyone buying from them for a bit. They probably can't resell the bottle I opened, but the other two are unopened and fine.

This has never happened to me before! What would you do?