Who is best supplier & What is Payment Term ? when any Co. decide stop operating with & what is the alternative's the company have when decide that?

AP section is very hard to manage but the basic PMT Terms the longest is the best , Then i can decide to stop operating when i feel that the sppliers is using me i mean the company as they are some palying in the outdoor with the purchasing section, always I MUST advice the purchase not to depend only on1 or2 but at least MUST have3 suppliers to compare between them to make the company always in the safe side.