Red flags include: prices dramatically below market rate, misspellings or inconsistent labeling, no lot numbers or batch tracking, vials that arrive already reconstituted (legitimate peptides are sold as lyophilized powder), unusual powder color or texture (should be white to off-white), and vendors who refuse to provide COAs or discourage independent testing. Also be wary of vendors who only appear on social media with no established reputation. When in doubt, test before using.