Application for multiple visa for one or two years

Maggie, do you have a supplier in PRC? If yes, you can ask her/him to issue an invitation letter to you. In this way, you can apply for a business M type with multiple entries for a year.
You should prepare the required documents containing your passport and copy of its data page, the application form affixed with a passport-sized color photo, and the invitation letter. And then submit your application to the CVASC to apply for it.

What kind of invitation letter ? To invite me to see their products or a letter stating that I am their regular customer to their company ? Normally I just source around for the products that I wanted and purchase . Thank you.

Dear, both reasons are okay. If you want to apply for business M type, an invitation letter from your trade partner in PRC is necessary.