Put suppliers next to each other on the same materials, so the choice is made on delivered price, distance and stock rather than on whichever quotation arrived first.
What a fair comparison holds constant
The same specification: the same grade and strength, because cement and blocks are not interchangeable across grades
The same unit: bags against bags, tonnes against tonnes, and the delivered rate rather than the ex yard rate
The same quantity: a rate for 500 blocks and a rate for 50 are not comparable figures
The same date: prices move, so a quotation from three weeks ago is a different offer from this morning's
Why comparison is worth the effort
Material is the largest single cost line in most building work, and the spread between suppliers for identical goods is routinely wider than the margin on the job. Comparing properly, on a defined quantity, is one of the few places where effort converts directly into profit.