Yiwu is biggest market-place in China (this says enough!), mostly concentrated on gift/decoration-like items, but there are also many other products catoegories, too.
It is definitely No.1 place to visit for your busines profile.

Guangzhou is also interesting, there are lots of clothes markets, and also other products, which shouldn't be avoided.

As frequent EU-China flyer, I recommend travel from EU to China via HongKong (this will save money for ticket), and Guangzhou is only 1.5h by train, where you can visit local markets, but also use it as transfer point and conveniently fly to Yiwu as your main destination.

I'm European living and working in Guangzhou and HongKong, very busy during October (Guangzhou & HongKong trade-fairs), but in November I'm free, so if you need any help, information or just tell us, I would be happy to help in any way.