It's a fine old plan!
My only concern would be going to an independent fish shop, miles away, and finding something incredible there, with no sensible way of getting it home!
There are 4 (probably more) ways to respond in this situation:-
1) "That is an amazing fish, but there is no way I can get it home safely from here. I guess that's just fate" - feels a bit sad for a while, then possibly gets home and realises that the amazing fish wouldn't work well with the fish already in the tank/doesn't have a tank suitable for the fish, and is comforted by the thought that the impulse purchase could have harmed the fish and left the fishkeeper in an emergency situation of trying to create a suitable environment for a new fish at short notice.
2) "That is an amazing fish, but there is no way I can get it home safely from here right now" -
feels interested in finding out more, takes pic of fish with label containing latin name, goes home and researches the requirements of the fish. Spends a couple of weeks on the research, decides they they can't keep the fish in a current community/can't buy a new tank/can't keep the fish correctly...(remaining actions follow those of option 1)
3) "That is an amazing fish, but there is no way I can get it home safely from here right now" -
feels interested in finding out more, takes pic of fish with label containing latin name, goes home and researches the requirements of the fish. Spends a couple of weeks on the research, decides they they can set up a suitable environment. Goes to LFS with information and asks if they can order it. Or decides to order the fish online for delivery.
4) "That is an amazing fish, but there is no way I can get it home safely from here right now" -
feels interested in finding out more, takes pic of fish with label containing latin name, goes home and researches the requirements of the fish. Spends a couple of weeks on the research, decides they they can set up a suitable environment, and that they do want the fish. Several weeks/months are spent doing further research and setting up a suitable environment prior to a long trip back to the store, with a fishy travel kit (battery operated air pump with some mature filter media in a small amount of tank water, polybox large enough to contain the fish in a bag, and anything else that could help). Travels back to the shop, gets the fish, returns home with everyone doing well, acclimatises new fish to new set up, everyone lives happily ever after.
Hope that helps - the general message is "don't buy fish from a distant store you've never visited before on the spur of the moment, as it results in the sort of chaos that we can all do without".