Every accredited certifying body maintains a public record of who currently holds its credentials — which means any trainer's stated qualification can be checked before money changes hands.
The United States Registry of Exercise Professionals (USREPS) operates a free public search covering exercise professionals certified by the NCCA-accredited bodies in its registry, and states its purpose as letting consumers, employers and healthcare providers confirm a professional's credential and its expiry status. Individual certifiers run their own directories as well — ACSM's ProFinder is one example. The registries' published guidance is procedural, not evaluative: confirm the exact credential name, the issuing body, and that it is current.