When sourcing a used capsule filling machine, you must prioritize the production capacity (output per hour) and the capsule size compatibility (e.g., #00, #0, #1). Ensure the machine features a high-precision dosing system (tamping pin or dosator) to maintain weight consistency. Check the material of contact parts, which should be 316L stainless steel to meet pharmaceutical standards. Additionally, verify the PLC and HMI brand (e.g., Siemens or Allen-Bradley) to ensure future software support and ease of operation.