Should the lowest-priced proposal always be selected as the winner why or why not give examples

The lowest price proposals shouldn't be always picked as a winner even if it costs lowly because the individual responsible for the decision should take other matters into consideration and whether what are the right decisions that he or she should make for the betterment of the company. Example of this is the lowest price materials offered by one contractor in which it is cheap but is not as strong as other materials they often buy, the one responsible of taking this account should ensure whether it is even right to use as their materials when he or she knows that it is not as strong as the ones they often used.