Pin down the exact species first
Every check that follows depends on knowing precisely which frog you mean, so start with the scientific name rather than a shop's common label. Common names shift between sellers, cover several different species and occasionally attach to the wrong animal entirely, while permit lists, protected lists and breeder records are all written against scientific names. A photograph of the frog you like, matched against reputable species profiles until you are confident of the identification, is worth an hour before any money moves. Once the name is certain, the legality question becomes answerable instead of a matter of opinion, and any breeder you approach will take a buyer who arrives with the right name more seriously.
Check the law where you actually live
Frog legality is mostly set at state level. Your state wildlife or fish and game agency publishes the rules for keeping amphibians: which species are unrestricted, which need a permit, which are prohibited, and which native species are protected from collection and sale entirely. Read the list for your exact species rather than assuming frogs as a group are fine, because a species that is legal one state away can be restricted in yours, especially if it could survive outdoors locally. Then check the layer underneath: some cities, counties and housing providers restrict exotic pets regardless of state law. Internationally traded species add one more consideration, since some frogs are regulated for cross-border trade and should come with proper paperwork from the seller.
What real captive-bred proof looks like
Captive-bred is a claim anyone can print on a label, so ask for the evidence behind it. A genuine breeder can show you the breeding adults, describe or show the tadpole rearing setup, give you the approximate hatch and morph-out timing for your frog's clutch and tell you what it has been eating since. Juveniles raised in captivity are typically uniform in size, feeding confidently on standard captive foods and free of the parasites and injuries that plague wild-caught shipments. Warning signs point the other way: mixed sizes and species in one lot, adults described as field collected, a seller who cannot say where the frogs came from, or prices for difficult species that seem too easy. Frogs from those sources often arrive stressed and short-lived.
Where to look near you
With the species confirmed legal, find the people who actually breed it. Established reptile and amphibian breeders, specialist shops and reptile expos are the realistic sources, and a breeder with a waiting list for a species is usually a better sign than one with unlimited stock today. Ask other keepers in local herpetology societies and frog groups which breeders they trust, and be prepared to wait for a clutch or travel a little rather than settling for an unverifiable animal. KinsLe's Pet Services Directory is a practical starting point for finding trusted local pet businesses and connecting with them, so your first conversation about the frog you want can be with a real local seller whose reputation you can check.