Examine certifications: Look for machining suppliers with marketplace certifications like ISO 9001
https://www.honkaistarrail.wiki/index.php?title=A_Step-by-Phase_Guidebook_to_Precision_CNC_Machining:_From_Style_and_design_to_Production_46596
Test certifications: Search for machining suppliers with sector certifications like ISO 9001, which assures good quality management methods are in place