Oh for sure, there are some shady ones disguising themselves as good. Thankfully there are ways to tell, all from my personal experience.That's good advice above, but unless you know the reputation of the online seller, be careful. I know of too many online sellers who buy the same guppies or poorly raised fish as the chain stores do, and resell them. I like to see the fish I'm buying, or to really trust the seller I'm buying from now.
I messaged the seller asking my questions, like the water hardness and pH to see if it matches my water and whether the fish were healthy. Seller was very happy to answer all my questions and was very responsive. I asked him if he was able to give me fry instead of adults, and if he could mix different strains and endlers x regulars. He was very happy to, and I think we all know why lol (wink wink).
I was to recieve the fish while I was working and nobody else was home. So I had to direct the parcel to my local post office. I let the seller know and asked making sure the fish would be ok. Seller reassured me they'll be fine, and how he got them from Thailand and how they spent a week in transit. Second time I got 4 more from him, Royal Mail ignored all previous instructions and left the parcel by my door where they could've been pretty much stolen. Seller messaged me back saying he'll write up a report and that I should the same, so we did this and RM took it seriously.
So yes, that seller was a very very veryyy good choice and I'll recommend him to any England based fish keeper.