In a general sense, we talk of all China suppliers as being genuine unless proven otherwise so far as we dont get into the thick of responsible china sourcing engagement. It is also true that no one can overemphasize the need to verify trading partners, let alone China suppliers. It pays to spend a moment to know the credentials of your partner before it is too late.
-Registered Corporate Numbers of China Suppliers
All China suppliers, regardless of whether they cater to export markets or deal domestically, must obtain a legal registration number for their companies from government authorities. The government agency entrusted with the responsibility of registering each applicant and according a unique number to each of them operates at all levels and across the nation. The agency, Bureau of Industry & Commerce, is the only agency entrusted with this responsibility of registering China suppliers which puts paid to possible confusions and chances for frauds.
Supposing that, China suppliers not being able to provide you with their legitimate and unique company registration number (should be on all their communication mails, in a normal case) even after reasonable amount of time and repeated requests, it is time to suspect them. Before you can conclude against them, you may contact the authorities at Bureau of Industry & Commerce or their respective provincial offices at www.csaic.gov.cn or Tel: 86-731-2891606. It is another thing that you may be required to write to the Chinese authorities in Chinese.
The official government website www.csaic.gov.cn also lets you download a list of China suppliers registered with them in your area of interest. This is quite a remarkable facility to have just when you are looking for a starting point.
Most of the China suppliers, on their part, are registered and are legally constituted companies. But this may not be sufficient to conclude that not all of them are genuine and can be good sourcing partners. However, this is a matter of intents of individual companies which can be better checked by time tested principles of business. You can run a series of checks to decide whether a company belongs to the list of genuine and capable China suppliers or not based on cross references and your own experiences.
Trusting internet directories may be risky, as many websites are known to manipulate supplier ratings artificially and forum members are often suppliers posing as buyers. http://www.sourcingreview.com/ is one place you can try checking for trustworthiness of China suppliers you are evaluating.