Effective Purchasing is a lot more than just finding the lowest price in the market. It is really about computing the total cost of ownership of a product or service from a supplier so that a rational choice can be made between competing suppliers.
Does supplier A or supplier B have the right goods or services, at the right price, at the right quality, in the right quantity, at the right place, at the right time for both the short and the long term?
From the point of view of the total cost of ownership, the low-price supplier may not actually provide the best value for you. Yes, the price might be low, but the volume demanded by the supplier might be much more than you can use in the immediate future. It could also be that you don’t have the warehouse space that the higher volume requires and you will have to spend more to rent or build additional warehouse facilities.