I have seen some "yellow" hammers. The yellow color is a fluorescent from some blue to ultraviolet light. In white light they are green and in 455 nm too so it must be a shorter wavelenght that makes that color.
I believe it is 420 or 405 nm. I am quite certain that with the exact light your coral will show up as yellow. So just ask extreme corals what light they did use when they took that photo.
I totally agree with you. Private sellers live by reputation and word of mouth, sot their pieces are top notch.I believe that at times is better to buy from private people than coral places, I bought one yellow hammer and it looks awesome and I acquired it from a private guy... some places want to sell and that's it
They can make it look any color with the right lights, filters and Photoshop. I run into the same thing. It's false advertisement and they all do it.