Not exactly what I would call "researching" a fish prior to purchase...
I did a quick google search on "yellow clown goby" and came up with this page:
http://www.saltcorner.com/sections/z.../Gokinawae.htm
It mentions that the goby resides in acroporas, but no mention of eating them.
Are you sure that the goby is to blame?
I'm sure that your LFS would normally take back a purchase that you're not happy with. (as long as you're on good terms with them)
Mitch