For using Alibaba payment services, there are some rules to follow. http://goo.gl/w8OehW
I think the supplier is talking about Trade Assurance amount covered.
For using Trade Assurance (samples or purchases), you must order over US$ 100
If you dont use trade assurance, there is no minimun order. Just negotiate with the supplier.
For samples I recommend to check company feedback and order without trade assurance.
For orders/samples less than US$ 100, you can use Buyer Protection. It is authmatic at Wholesale option.
Hope this helps