This is Frank ,from YOULISN factory ,We are manufacturer of massage gun and one of Carrefour and CASADA,LINGNING supplier, We can provide professional R&D design department and provide tech support , All our items is coming with certification ,as honest manufacturer, we never crook our customer for you and for us. So we have professional production line and stuff who is making nice quality in short time . we can send you samples for testing at any time ,please do not hesitate to contact directly at any time, my time is serve to you, looking forward to your reply and cooperation!