I won't buy one under 10-12 inches. They are very hard to feed at the size you had, and need to be in a small calm tank with no other fish so you can give them as good a chance at getting food as possible.
They can be slow to find food and take awhile to eat, so they need to be by themselves and the tank needs to be filled with various live foods like ghost shrimp, small aquatic worms and bugs. With a pbass and arow they will be outcompeted for food, and they are also shy and may be scared to hunt.
If you try again with a small one keep it in a small tank by itself, with a sandy substrate, low lighting, and plenty of decor. And you are best off ordering from a vendor that already has the individual eel on food. Don't listen if they have a large group and say "they" are eating, because they're not likely watching every individual fish and they may not all have fed.
If the vendor claims they are eating flake or pellets at that size, they're likely not telling the truth or mistaken because they will almost never take to flake or pellets, especially for the short time they're with the retailer..