Replying to [tina liu]:
Your are pointing an excellent point as this is all about the effectiveness of trade portals like alibaba. Patience is a point to consider. But i think that you should bear in mind that many buyers don't use only trade portals and they use other channels.
Internet is not the good channel for all the commodities in B2B relations. Alibaba is considered to be a very good reference in internet based business in the world.
Then to make an idea i would suggest to look in your category how many suppliers are registered on Alibaba and compare it to the suppliers in other categories; it should be comparable depending of your category otherwise, if you are too many suppliers, compare the number of the paid members to the buyers and the buying inquiries. I can't give you a ratio, but you should be able to appreciate if competition is high between suppliers (B or D category of inquiries) on alibaba in your category. If you feel this is not just competition or possible low number of transactions (as it seem that A group is also important), then you should change trade portal or be patient or seek buyers through other channels than Internet.
In case B and D are important, i would suggest to review your strategy and make a kind of assessment of your competitors either on alibaba and other channels and make a good positionning either on your prices and either your services and, why not, products.
GOOD LUCK