I have some good dealings and bad dealing with some LFS in south yorkshire...
i dont want to name and shame any right now.. but i have even bought some pleco from a couple of lfs just to get them out and rescue them as they have been underfed and not looked after.. they have turned out to be some of my best fish.....
i also lost 5 out of 6 cory's i bought from a rather reputable lfs recently....

and all my water parameters seem ok... i try to check them twice a week...
could be over stock due to my pleco explosion right now but I doubt it as two fluval filters in their are fully matured and all my tanks have regular water changes.....
the lfs would not replaced the lost fish so i am out of pocket, (not shaming them right now) which isnt good as i am out of work and used my birthday money on them

the same lfs won a practical fish keeping award a few years back, but guess things must be slipping recently...
only thing i can think of is the albino and panda cory i got were very young amd not fully quarantined, possibly over stressed..

i find the new set up of pleco's at viscum garden centre at barnburgh near doncaster, is quite good, they have a large selection right now.... can be a little pricey... but ask for Warwick coz he is good and very knowledgable....
and tell him Lj/Lee from the Dearne area who breeds pleco and guppies sent you... and I am sure he will look after you ok...