What would you expect your LFS to do?

This could happen at any LFS. I would medicate the fish. About 70% of the fish I have bought were ill. There is no way to prevent it. It just sounds like ich which is common and easy to cure.

Well I am sure that isn't everyones experience but I think most people have brought a sick fish home before.

Well, I've only bought fish from 3 different Petsmarts and 2 local fish stores, but I've never once bought a sick fish. I only buy from the two respectable LFS. First, you should always be sure to check fish out before you buy. Make sure there are NO dead fish in the tank, same species or not. Avoid swollen bellies, swollen eyes, lack of balance, white spots, red spots, sunken bellies. And pick your fish out, don't let them just fish in a grab out any one they please.

If they won't take them back, I probably wouldn't continue to use that store. After all, the fish had ick before you brought them home. Also, it's really the stores fault if any of your other fish die, but that's why you should quarantine your new fish(listen to me preach, I've never quarantined a fish in my life! ) But you can't make them take them back.

Best thing to do is slowly raise your temp to about 84 degrees, and add some aquarium salt, to about 1 teaspoon per gallon. Ick really is an easy problem to fix, if a bit annoying.

The ich treatment should be at 86F. And run the treatment (with proper water changes) for three weeks. That will make sure you won't get any more ich from the current fish and tank you have.

The plants will be fine, don't worry

I recently treated for ich in my tank and the plants are completely fine. I used 1tsp/g pickling salt and turned the temperature up to 86F; all the plants and all the fish came through just fine.
And no, it won't hurt the biological filter - that's one of the things I like about this treatment; it's not hard on anything but the parasites.

Hmm, my fish store quarantines any fish they suspect of ich or velvet and do not sell, until absolutely healthy. I know they would be taken back and I'd be given a store credit. No doubt about it.

There should be a reasonable guarantee for the fish's life expectancy once purchased, a week or so anyhow.

I agree with archangel, you should eyeball the tank, and inspect each fish once in the bag and again at home. My LFS checks each one before the sale using a magnifying glass.

The good thing is you can treat this pretty easily as per the advice given. Sounds good.

You do get a lot of sick fish, so it pays to be wary. Unfortunately in our town at the moment there appears to be only three places to buy fish. A large all pet store, a small all pet store and a specialist tropical fish store. We've had the most trouble with the largest pet store, NTD and various things. Their prices are also the highest, tho we tend to go there on occasion as they have the best range if you 'really need something'. The other pet store is okay, tho we did get black neons with ich there. They are out of the way so don't use them much anyway, tho their prices are better than the rest on some things. The fish only store is more out of the way than the main pet store and doesn't have the range, but mostly has the lowest prices and the best quality fish (tho not the range). We only buy live fish there now as they do know a little more (tho they will still stretch things to sell a few more fish).