Those are pretty horrid conditions, but I've seen much, much worse.
I'm guessing they just have everything mislabeled because their employees are too lazy to label them correctly. Ask the store manager if they have the previous snakes you saw in the tank (Albino Ball Pythons). If the do have them in the back, I'm sure they will tell you.
I'm pretty sure, they wouldn't have sold them for $15 each if they have a Pastel listed for $400. Again, I am guessing that they are just too lazy to clean the enclosures and properly label them.
I do agree with another post I read, if you are interested in an Albino (which you said you weren't), buy one for a reputable breeder. With a store like that, there is no telling what else you can bring home with the snake (IBD, Parasites, RIs, etc.) So if you are truly not interested in buying one for personal reasons and unwilling to take the risk, leave them for someone else, just imo though.
As for their housing issues, print off some caresheets for the owner and offer to help them clean and set the snakes up for free. It's just a matter of donating your time and energy and most pet stores will accept. Especially smaller stores, most of them don't know they are doing anything wrong. Education is the key. If they can't keep up with it after educating them and donating some time, they are a lost cause and I would completely cut ties with their store.
Just a side note, anytime I go to handle someone else's collection (pet store or personal collection), I change clothes and shower before even walking in the room with my own collection. You never know what can hitch a ride on you.