A reliable supplier answers specification questions, states MOQ and lead time, and can explain packing and shipping. Slow or inconsistent replies are a risk signal before any deposit is paid.
Ask for a sample when the SKU matters. Sample cost and freight should be agreed in writing. A sample does not replace pre-shipment inspection, but it reduces surprises.
For first orders, keep the SKU list short. Confirm voltage, plug type, labeling language and battery rules for the destination market before production starts.