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As an avid book collector I have often been caught out by books which have been reprinted under different titles with different covers or simply republished with different covers and I wondered if this would be the place to warn people?
For example I have over a few years purchased three books on Reiki all with different titles and covers yet each book is identical inside! I have actually gone on Amazon and left a comment to the indicate that these books are identical to warn future purchasers.
Another example I saw yesterday is Sue Lilly's The Crystal Healing Bible which is a republication of The Crystal Decoder except it does not include the charts.
Hope this helps! 
This is really irritating!!! It's just a gimmic to increase their sales 
This is a trick that publishers use (rather than the authors directly). If they know a book was a good seller when it first came out, they give it a 'new lease of life' by republishing it under a new title or format in the hope that it will look more up-to-date and be picked up again by new customers. Of course this can catch out those who have already bought the book under a different guise, so it's good if people are warned.
All Love and Reiki Hugs