I would like to offer two options, you may elect to do one or the other, but doing both would not only verify that the supplier is a legit business, but also confirm they can meet the quality level you desire.
Type 1 “Operational Due Diligence”
An investigation of a business prior to signing a contract to ensure the company (supplier) signing the contract is who they say they are. For example, do they really have 1000 employees, 50 million USD exports, own the factory 100%, have happy customers, good financial situation (will not close doors suddenly) and so on.
Type 2 “Quality Audit/ Factory Audit”
This service is designed to ensure the supplier has the equipment and experience to make a given product.
Audits can be conducted by the buyer, but usually 3rd party experts are hired to do the audit as it is a specialized skill. You wouldn’t ask your sales team to do engineering for example.
In my opinion, doing the due diligence AND quality audit is an essential step when sourcing from China. Perhaps I am jaded after 12 years living here, but I assume the worst unless proven otherwise. Trust BUT verify.
For your reference, I have used the following companies for type 1 and type 2 services above.
If you like, I can put you in touch with their representatives so they can reach out to you and explain their services in case you need support.
Let me know how things work out for you.