A lot of the overgrown plecos end up in show tanks in restaurants & hotels. Where they are happy to only have a few large fish on display and can afford the large tank & filtration!
In was in a restaurant on Friday, where they had 2 large plecos (over 15") sharing the tank with various goldfish (koi?). The tank was at least 8ft long and 3ft wide.
I agree that people should investigate the fish before they buy them, but think equally the LFS shares some of the blame as they should advise the person before they buy.
Although I would never buy a fish from Petsmart (Petco), they at least display the full name, scientific name, eating requirements, shoaling/agressive and the final length for all the fish on sale.
Jazz_UK