How we can avoid potential purchasing related risks, especially financial risks. Most of the suppliers required advance payment?

Suppliers require advance payment for two reasons1: they dont trust you or2: the business you are providing is too small for payment terms.

In situation1 the company should have regular transparent meetings with the supplier where in you ask their advice to tap markets. in other words make them feel like they are integral part of your functioning, and ideally they should be.

For situation2, make supplier contracts promising purchase of certain amount worth of goods if payment terms are given this gives the supplier an incentive to give you payment terms.

these two above points can be done in combination and can prove very effective