I have never bought fish online. Just something about it that i quiet cant het my head around. I like to buy from various different LFS. Id rather pay a couple of pounds extra and support these shops than go to a big buck store. Here in London a lot of great LFS have closed down. It really has hurt the hobby.
I dislike buying online, but have the advantage of having a close friend who is a seller. I know he'll only send me stable, healthy fish representative of the best of their species. But not many people have that.
From what I've heard of the UK hobby, you still have good shops closer by than in North America. For example, it takes me four hours to get to the nearest large aquarium store, and they have the stocking of any good urban store - no more, no less. To go to a city where I could visit several stores, I would need nine hours of driving each way. I get the feeling if I drove 9 hours in a straight line in England, I'd have lots of fish around me as I sank into the North Sea.
That changes things.
I used to have to cut through the northeastern USA a lot from the 1980s to the 2020 period. At first, most decent sized small cities there had decent local stores. Some had two or three - not outstanding, but with different fish as they competed with each other. In a very short period, those stores vanished, replaced by 2 major corporate chains. If you went in to look in town B. the 12 tanks on the upper rack had exactly the same fish in them as in towns A, C, and D. Tank one was this fish. Tank two was that. The uniformity and lack of choice was hobby killing.
We blame the internet for killing the North American hobby, and it has done a lot for that. But those corporate chains, with their MDonald's menus of fish species have probably done more harm.
We have them here, but for whatever reason, they haven't been able to create the monopolies they have there. and what I see is they're now eating themselves. The endless offerings of glofish and hybrids mixed with young fish that'll outgrow tanks aren't selling enough, and dog and cat food is getting the space as they close aquarium racks. Some little stores are reappearing, though the going is tough. That's in Canada - I don't know what's up in the US anymore.