Do not buy a puppy from a pet store. Bad all around.
If you’re set on a Maltese, try to find a Maltese rescue. Most breeds have rescue organizations, where purebred dogs end up because it was a bad fit with their previous owners, and various other reasons. They may be able to direct you to a rescue Maltese dog, but in any case they will know the reputable breeders.
The thing is that rescue organizations can also harbor crazy dog people who will blacklist a breeder of Maltese if they also breed mutts like malti-poos, and the other various things. Their attitude is that no reputable breeder would dilute the breed that way. Now I am not wholly in favor of breeding mutts on purpose, but I think breeders can do that and still be “reputable.”
What you want to see in a breeder is someone whose breeding stock is kept in the home. A lot of them do co-ownership, where the dog lives with one family until it’s time for its breeding obligations, and then it goes and services the female, if it’s a stud, or if it’s a female she stays at the breeder from the time she gets pregnant until the pups are weaned.
Bad breeders keep their dogs in conditions where they don’t get a lot of attention, they have too many dogs, and the dogs are not well exercised. They are called puppy mills because they breed without regard for improving breed standards. They’re just in it for the money. They don’t improve their breeding stock with things like, for instance, showing them, entering them in dog sports and obedience competitions. These are the people who sell their puppies to pet shops. Reputable breeders screen the people their puppies are going to.
Find the local Maltese rescue. Maybe you don’t know how to assess breeders, but you can talk to someone or email them and you’ll probably be able to discern if they’re a concerned individual or a mouth-foaming dog fanatic.
Also, if this is your first dog (I don’t think you said), get an older dog. Puppies are extremely cute but they are a lot, a LOT of trouble. Maltese dogs are cute at any age!
ETA: Actual red flags for bad breeders: They won’t let you see the parents (both of them), they don’t health-test the parents for any genetic diseases endemic to the breed (I don’t know what they are for Maltese but it’s easy enough to Google); they let their bitches have more than one litter a year; they don’t hand-raise the pups; they don’t screen the pups for temperament; they don’t screen the buyer for compatibility with the pup; they let the pups go to their new homes before the age of 8 weeks. Possible red flag: They ship puppies to distant states; they breed designer mutts.