Im offering this as constructive criticism, so please dont feel that im speaking of you on a personal level. The biggest rookie mistake you are making is that you are betting the health and well being of your tank on what-ifs and "i hope"s. dont ever buy things in the sw
hobby in the HOPES that itll work/eat/ stay small/etc. only go with well educated decisions and information. As trustworthy and reliable as your lfs
may seem, you have to remember that they are a business first. Sp they will tend to bend some rules and guidelines if it means selling something. ( its not a horrible thing, just the nature of business). Us salties here on AA only want to see your tank thrive and you smile... We dpnt need your money to pay bills, we dont need your business to stay open. So 9 times out of 10, the info here is more reliable.
Also id just like to say that i personally know that its extremely hard to accept that some fish are just too big, but each and everyone of us goes through it and as long as you stay on track, youll be happy in the end. (i wanted a blonde naso tang for my tank but he gets too big)