I know Mandarin and speak it well. Should I contact them using Mandarin or English? Should I meet them face to face online to verify their legitimacy?
Look at the way they write, does it seem like your Mandarin is better than their English? The answer should be obvious from there.
Yes, makes communicating so much smoother, less space for misunderstandings.
It is essential to have a Mandarin speaker/ translator with you when conversing with manufacturers in China. They make it that much smoother when building relationship and pricing. Without them, you will be paying X amount more than normal knowing that you are a foreigner. Face to face will get you the best prices
IDK about the language, but of all the adjectives I’d use for Alibaba sellers, legitimate is not one of them. You go to Alibaba to buy Nika shoes and Aple phones.
English, Spanish, Thai, Dutch, etc.