Three quotes come in. One is materially cheaper. The temptation is to treat the gap as a saving, when almost always it is a difference of opinion about what the job is.
The cheap quote is usually cheap for one of four reasons. It has priced a smaller scope, because the contractor has not investigated properly and is quoting the symptom rather than the cause. It has priced worse materials, which is invisible on a quotation and obvious in 3 years. It has priced a thinner team, so the work takes twice as long and someone else pays for the disruption. Or it is a number chosen to win the job, with the real price arriving later as variations, once the scaffolding is up and the client has no alternative.
None of those is dishonest. The market rewards the lowest number, so contractors produce low numbers. The client who chose on price then discovers that the cost of the work was never the cost of the quotation.
The way out is not to stop caring about price. It is to make the quotes comparable before comparing them — to specify the job precisely enough that three contractors are pricing the same thing. That is unglamorous work, and it is where almost all of the actual saving lives. A properly specified job tendered to three competent contractors will beat an unspecified job tendered to ten.
The cost of the work was never the cost of the quotation.