Tell me, do these LFS' have a warranty on their fish?
Do they test water on tanks, and encourage you to bring in water to be tested before adding fish, and before they sell you one? A store with a good warranty is likely to do this, so they have some confidence in your tank, and not just what you are telling them.
An LFS is in the business of selling fish, and there are few who turn eager customers away, especially if they know you will be back next week for more. Many don't have a warranty and as soon as the money is exchanged, it is your problem. This may be a stupid employee problem, or this may be a scam company with an eager customer. Many LFS' are like that, a fea aren't (I also worked at an LFS, BTW, and have a grad degree in marine invert zoology, so be careful of the assumptions made about the employees).
You need to read up on types of fish for that tank, acclimation, filtration, etc. This is a hobby that requires an incredible amount a patience and self taught education. Without it, you will fail, regardless of the money you put into the system. You don't go in to buy a car without doing some research- and knowing that the salespeople at Ford aren't going to say "ya know, you really shouldn't buy this car, you only have a two car garage and its full" or "you really need to go over to the Chevy folks and look at their truck instead." These are animals, and it is the buyer who bears a good deal of responsibility in what they buy.
In that size tank, with predators, you are looking at MAYBE 3-4 fish, depending on what they are, and certainly not the panther grouper. You need to think about fish you can keep long term, and that won't eat other fish. What sort of filtration do you have, protein skimmer, etc? Live Rock? Sand?
I would find a new store, really really fast. I would even consider writing a letter to the better business folks in your area, and file a complaint, once you learn how wrong they were...but in exchange you must take responsibility and learn from this, and follow the advice given in this thread. You must read and research before adding anything to that tank. Ask on this board where people go in your area. The stores you went to had you in the palm of their hands, and they took advantage of you in a BIG way. BIG BIG BIG WAY. How much did they make off you??