Suggest purchase a pet fish from a four-star online store?

It is a lot better to buy fish from a local petshop, close to where you live. You can see the fish you buy and the shorter time it takes to bring the fish home from a shop will most likely stress the fish less, so their health will be better.

I understand why you try to avoid the large petshop chains, but it still might be better to get your fish there than it is to buy online.

If you buy fish online you risk the fish dying during transport if any delays happen (they DO), one does not know what stress the fish is exposed to during transport, like heat, cold or bumpy ride.

Most online shops will not send live fish as mail or cargo because the transport takes too long - even if the transport goes as planned, the transit time might be over 24 hours.

Goldfish grow too large for you to keep them in a fishtank, to keep one single goldfish you need a tank of 75 liters and for every additional fish you will have to add 50 liters in tank size. More details about goldfish could be found at the relevant article on Wikipedia.