They may ask you to install "configuration profiles." Installing unsigned or untrusted profiles can expose your device to malware and data theft.
The version of Cydia it installs is typically a "web-clip"—essentially a glorified bookmark pinned to your home screen—rather than a functional system-level package manager.
Many sites force you to download and play several mobile games to "unlock" the code, which only generates ad revenue for the scammer without providing any real jailbreak. Legitimate Jailbreak Alternatives
Real jailbreaking tools are and developed by known security researchers. If you want to customize your device safely, look for these verified resources:
Drainage Cheshire