Why Bids Vary So Much
It is common to receive bids on the same project that differ by 30 to 40 percent. That usually does not mean one contractor is cheating you. It means the bids are describing different projects.
A lower bid frequently excludes work the higher bid includes: permits, engineering, allowances set unrealistically low, or simply less detail assumed in the finish work. The gap shows up later as change orders.
The only way to compare bids meaningfully is to compare line-item scopes, not bottom-line numbers. If a bid is a single lump sum with no breakdown, you cannot evaluate it.