There are a few LFS's that I trust, but that comes with experience too. The best thing you can do in this hobby is research each item you'd like to put in your tank before you buy. Then you have a better idea of what you're in for, what to expect, how things should look when you're ready to buy, and the best benefit, you'll know which people at which stores know what they're talking about and are willing to share the info with you.
I think if you can take it back, that would be best at this point for the nem, to me it's not worth the risk, but that's just my opinion.
Another option would be finding someone in your area that has an established mature tank and getting it to a home that may be better suited for it. A lot of the local reefers in my area will buy or trade merchandise with each other. That's also a great way to get to know the people in your area that are into the hobby too - they're also a great source of information.
This is also a good place to ask questions, get answers, and research the things you'd like for your tank. Welcome aboard!!