yeah np that is what we are all here for, and i wouldnt really trust the manager, just watch them for a while and make sure its being really active and showing lots of nice color (and has design with its fins and iridescent body scales since im assuming you will want an all male tank to avoid breeding issues and get the most color specimens) and try and see if he poos and see if it is normal or white/stringy, and yeah you can ask them to feed them if they will do it but if not then just get the one you think is the most healthy looking and keep a close eye on it and treat your tank for parasites at the first sign of white/stringy poo (this is why its good to have a small tank set up for quarantining new fish, especially ones that you know are prone to diseases and then if they are sick it is cheaper to treat as well)