Tricky Sales Letter
Its not a good practice to do such kind of sales letter for reputation. After a lots of negative response to this product the author came up with apology. Many bloggers like Darren Rowse , John Chow were promoting this product and had a very bad response to his promotional post. Darren is very much accepted by his community and he has about 45K Feed readers. There was an scam alert post by Mark of 45n5 which actually triggered the information to the buyers.
I believe if you are going for a long term sales of your product, you should mention terms very clearly and the buyer should be aware of the payments that needs to be made. They should never feel that they are trapped or fooled.