The five features that separate a reliable China soundproof phone booth manufacturer from a reseller are: (1) a complete in-house industrial chain, (2) dedicated R&D and a diversified product line, (3) verified acoustic performance backed by CE, RoHS, and ISO compliance, (4) real OEM/ODM customization capability, and (5) proven export logistics with after-sales support. Buyers evaluating suppliers should confirm all five before placing a bulk order.