Q: I've heard that a different headline would pull up to six times more than another. Is this true?
A: A headline change can certainly do that. Headlines (and, in a sales letter, the P.S.) are read first, so that's where you'll see a good deal of impact. Even changing a single word in the headline can make a significant difference. Decades ago, the legendary John Caples increased response 20 percent by changing "How to repair cars" to "How to fix cars." Sometimes surprisingly mundane changes work wonders. An educational institute for bankers once asked us how to get more branch managers to respond to their newspaper ad. We suggested simply adding the words "BRANCH MANAGERS" in large type at the top of the ad, leaving everything else, including the headline, unchanged. Replies shot up.
Q: Should we tell the client how they may feel about a collectible product? For example tell the customer this product will take your breath away or instead say this product is breathtaking.
A: "Breathtaking" merely describes the product, whereas "take your breath away" describes the effect on the reader, so it makes sense that the latter might pull better. BUT: what seems to make sense often fails in real life. It makes sense that a product priced at $24 would outsell the same one priced at $29, but the opposite is often true. So, rather than try to reason which wording will sell more, you can know by doing a split-copy test. (I assume you're dealing with a headline. If the wording is buried in copy, I would stress over other things first.) That said, I can't help observing that neither term is particularly convincing. Can a collectible really take one's breath away? There may be a more believable, more compelling claim as to the effect your product will have on its proud new owner.