Quoting from [ameelab]:
On Alibaba how to check any company detail when they contact me?
Well, since they contacted you through Alibaba, they should have a profile set up with all their company information, just go into your messages and look at their senders card to see what it says. If they don't have much listed, contact them directly to get their website, address, phone number, and other details you feel might be important. Then you can start your basic due diligence checks:
1) Verify their address, phone number, etc. Lot of ways to do this, google their info see if information you find online is consistent with who the company says it is. Call them on their phone number. Cross reference their information with other known trade sites.
If they are indeed a registered company, they'll usually be listed with whatever local government agency regulates business registration.
2) If they have a domain, do a whois check to see who it is registered to, whether to the company or just some person.
Those are just a few of the first steps to figure out whether a company is who it says it is, but hopefully it'll give you an idea of what you need to do.