Its not so much the degree of difficulty as the price tag doc. In the case of petco if you go in the evening after the regular aquarium guy clocks out one of there lackeys will be there and they are easy to confuse.
In the case of the powder brown I just pointed at him and asked "how much for the tang?". She just started looking at price tags until she saw one with the word tang and lucky for me it was a yellow tang. PB for the price of a yellow, could not pass it up.
Actually petco has the best prices in my area and all the LFS get there fish from the same wholesaler in my area. If I am looking for something specific fish wise I usually arrange to pick up on the morning it arrives at the retailer before it even comes out of the shipping bag. I know this goes against the usual advice but IMO my odds are better if the fish sees one less screwed up holding system and goes straight to me.
Were the LFS are concerned in my area the holding tanks mean either parasite exposure or massive doses of copper. My philosophy on this is just give me the dam fish before you have a chance to kill it.