I personally only use mail order for fish I can't find in the stores (either LFS or big box). I would never buy fish from a place like Wal Mart (really a place that sells groceries, tires, toys, etc. should not also sell fish), but I don't have issues buying from the big box stores like Pet-co or PetSmart. (I actually used to work for one). Our local Wal mart had to stop selling fish because they couldn't keep their tanks clean enough. But, at the big box stores, at least they are supposed to sell pets, and know about them. Some of the stores do a better job than others, and some workers are better than others. I used to work for a big box store. Our store (and all the others in our area) had an exclusive relationship with our fish provider. It was a very large scale breeder in FL, I think. I'm sure it served most of Our stores on the east coast. We got our fish in once a week, and our fish were on 'auto-replenish' meaning we got more fish in based upon what was currently in stock to keep us at a certain number of each kind of fish. (we used to be able to order our own fish, but that got switched to make all stores more uniform). Other than having more than *I* thought we needed of some fish that didn't always sell well, or *I* thought were inappropriate to sell, it wasn't too bad. I knew all about fish (of course), and tried to make sure the people in my department did too. I also told them that if they didn't know to find someone who did and ask rather than give out wrong information. Sometimes that worked and sometimes it didn't. Often, problems arose when they would sell whatever the customer wanted with out asking questions about their fish tank and setup. I always asked, sometimes, an experienced fish keeper would get upset, but more often than not, I would safe a few fish lives by not selling 20neons for a five gallon tank. Of course there were regulars, and I wouldn't give them the fifth degree, I'd just sell them whatever they wanted, knowing they knew what they were doing. If you get your fish from a big box store, visit it regularly. Find out when they get their fish in (it's usually the same day each week). Try to buy the day before the new fish arrive, so you know the fish have been there a whole week, and are still alive/healthy. If any fish in any tanks are sickly, wait until they all look o.k.--all the tanks are connected to the same filtration system. Talk to the fish person (likely the same person who takes care of all the other animals), see if they know about fish. Some big box stores can order special fish, some can't. (PetSmart can't but they get special fish called opportunity buys that change every three months. When it gets close to the time they change, the manager will know what the next batch of opportunity fish will be. Pet Co may be able to order special fish. Not sure about the others.) I bought fish all the time from the store I worked at, and never had a problem. I also bought from our sister stores (nearby stores of the same chain), and occasionally from our competitors. (other big boxes). I also shopped at LFS that weren't big boxes. The big box stores all have a 14 day guarantee on the fish they sell (not on fish already in the tank), so if one dies you can get it replaced or refunded if it is within two weeks. They usually require a water sample, so they will replace only if the water is good, otherwise they refund.
If you are really against buying any live fish from a big box store, then see if you have a local fish club. Members there may have fish for sale that you are looking for if they breed fish. If not, you may find someone willing to go together on a mail order, which will cut down on the shipping cost. Otherwise, since you are doing a fishless cycle, you will be able to add all your fish at once, so find a source that has all the fish you want and buy only from that place. Then, you will only have to pay shipping once.
Emily