I need a business visa to China

Hi, I'm a business man based in Abuja. I've been a banker for many years until last year when I started business. Over Alibaba Express, I got an invitation later for a business visit to Shenzhen but I was told to bring alongside a Ministry authorization letter with my invitation letter. When I asked the company about it, they told me there's nothing as such. Now, I really do not want to go on invitation because I don't seem to trust the people I've been communicating with online. What I want is a straight one for business so I can have the liberty to explore the various products that abound in that market. How can I get it so I can make my journey in January 2014? What are the requirements as my finances can handle whatever business decision I want to make there? Awaiting your prompt response please. Thank yo