I often go to P@H in Portsmouth, the tanks are well kept, and fish stock look healthy, ive seen on a few few occasions when a customer has highlighted to staff that a particular fish is looking ill, that fish is then taken out back to the quarantine tank out back, each time they ask if the tank is matured, what size it is and who are its current occupants.
ive seen them refuse to sell fish to people because they just walked in and said i want one of those one of those 2 of those and "ohh they look good give me some of those" that staff member said i cant sell you all those fish and half of them arnt compatible together, "how long have you been keeping fish for" "what fish do you currently have" & "what size tank" i laughed when the chap said it was a 60l tank that was currently sat in the back of his car that a friend gave him, apparently his friend had recently taken up fish keeping and all the fish he bought kept dying within a week of getting them, and he couldn't be bothered to get any more fish.
not all of the staff are fish experts but do their best to help and if they cant answer the question will go find a colleague that can, failing that i have seen one member of staff go back to a customer saying she couldn't confirm what size a fish could grow to, and she couldn't seek advise from another member of staff at that time, she turned to me to ask if i knew and said to the customer i was a regular and a little knowledgeable, i didn't know the answer tho she then said hang on a min ill be back in a sec, 2 secs later she pops back round the corner with a guide to tropical fish book that they have on the shelf for sale, gone through that and brought up the particular fish and informed him that fish he was looking at would be a squeeze in the tank he had, it could just be done but if it were her she wouldn't. that chap ended up spending a little more time with the girl looking at fish and what she couldn't answer she still had the book i hand to refer to. i think i saw that chap walk away with no fish but a book about tropical fish so he could do a little research to see what would be suited to his tank.