I am Karina, engaged in selling agar agar in Russia, thus, it is extremely important for me to select a reliable supplier of agar agar.
Google “Website”
While Googling a company website, there will be attached links along with the website on result page. It is an effective and reliable route to judge company scale and brand awareness since not a single company is able to impact Google’s objective valuation towards any company.
Exhibition
agar agar suppliers will never ever lose the opportunity to communicate with customers face to face on exhibitions. Although with rapid development of the network, some people choose not to attend exhibitions, while substantial companies still avail these opportunities to meet their clients and looking for potential clients.
Therefore, exhibitions provide a efficient solution to find agar agar good suppliers: Visit suppliers’ websites to see their participation in the exhibitions.
Google “Company Name”
A renowned company name usually shows a great deal results on Goolge Search, because its company name is frequently searched by their customers or cited by other web sites.
Take “Foodchem International Corporation” as an example, as has been showed in the below picture, there comes out more than 298,000 searching results on Google. 
Location
Generally cargo takes ship delivery; thus, sustainable trading companies tend to set their sites in coast cities, such as Shanghai, Qingdao, and Tianjin in China.
Certificate
A formal operation supplier of food additives normally passes ISO certificate as well as other well-known certificate like halal, kosher, ect.
Company Name
As a professional trader or manufacturer of food additives, normally its company name has food, chemical, additives or other key words in it. Other trading companies who have affairs in all fields, usually performs unprofessionally.
Warehouse
Warehouse is also important for agar agar suppliers, agar agar traders make judgments through agar agar market situation. On one hand, while agar agar is in the upside, traders purchase bulk agar agar for storage, and sell with the price advantage; On the other, vendors need to keep cargo in warehouse in case customers need LCL loaded.
Foodchem International Corporation owns an EDC warehouse in Shanghai, an advanced warehouse system which only few trading companies in Shanghai can provide, it avails fast delivery within 1 week.
Supply of Products
Compared with Manufacturers, other than service advantage, main advantage of trading companies lies in being able to provide various kinds of products. For example, when we would like to order agar agar as well as several other food ingredients, trading companies becomes the best choice, since unlike factories, traders can provide one-stop service and have greater bargaining powder which permits a lower price.
Of course , we can purchase agar agar directly from manufacturers if the volume is large enough, but it won’t be a bad choice if we keep in touch with some large-scaled traders. Because once your long-term-cooperate factory is in short of agar agar , we can turn to trading companies, who can help to find other suppliers shortly or even direct supply agar agar in no time.
As far as we know, big suppliers of food additives and ingredients can basically provide more than 100 kinds of products, among which, Foodchem International Corporation are able to supply overseas customers more than 300 kinds of food additives and ingredients, plant extracts, nutritional supplements, apis, etc.
http://www.foodadditives.com/Thickeners/Agar-Agar-Powder.html