Legally, only Group A travel agencies may operate tours abroad from Türkiye. The TÜRSAB website must list every agency's name, registered trade name, website and phone details. You can look agencies up here: TÜRSAB agency search (in Turkish). Appearing on the list is not an absolute guarantee of trustworthiness, but we strongly advise against booking with agencies or websites that are not on it.
TÜRSAB also publishes a list of agencies whose licences have been revoked: Agencies with revoked licences (in Turkish)