When a business owner in Phoenix sends the same set of plans to five contractors, the five bids that come back can look like they are for entirely different buildings. According to Mike Marden, a registered architect, licensed general contractor, and founder of the Phoenix-based integrated design-build firm WDS, the wide spread in numbers rarely stems from contractors trying to take advantage of owners. Instead, it usually traces back to project fit and the amount of room for interpretation built into the bidding process itself.
Marden, who has observed the bidding process from both sides for decades, says the variation often starts with what contractors actually examine. If a bid is based on a preliminary walkthrough rather than a finished, detailed set of plans, there is already ample room for wildly different interpretations before a single number is written down. On a site walkthrough, what one contractor sees, hears, and is told can differ from what the next one experiences, and that alone can start the variation. Even with a full set of plans, the numbers can still diverge based on how much time and attention a contractor plans to spend on the project, a difference that shows up directly in the final price as adequate or inadequate supervision, management, and overhead.
A bigger gap often comes from what gets left out of the scope. Some contractors visit the actual job site conditions and some do not. If two out of five bidders skip that step, they are pricing a different project than the other three, even though everyone received the same paperwork. Special instructions, separate exhibits, or desired exclusions can also be missed by contractors who are not reading closely, which widens the spread even further.
Owners often assume the lowest number is the safest choice, but Marden says the real problem is usually that the bids were never in a comparable format to begin with. He recommends asking every bidder to break their proposal down into separate scopes. Without that breakdown, markups like overhead, insurance, and taxes stay hidden inside a single lump-sum number, making it impossible to know what is actually being paid for. For larger projects, he suggests separating a project into its logical phases first, such as interior work versus site work or landlord work versus tenant work, and then breaking each trade out individually. That includes asking every bidder to detail their supervision costs specifically, since Marden considers supervision one of the biggest drivers of price differences between contractors. Some contractors provide a daily on-site quality control supervisor dedicated to the project, while others may just have someone occasionally driving by to check the job site.
Marden also identifies red flags worth slowing down for. A bid that looks too good to be true often is, and the first place to look is not the number itself but who submitted it. A one-line or quickly assembled bid is a warning sign. He recommends checking whether the contractor has actually done this type of project before, since a company skilled at building houses is not automatically qualified to build a medical office or restaurant. Photographs on a contractor's website can indicate their true experience, and a missing project schedule is another warning sign, since a contractor who has not accounted for the full duration of the job may not have built enough into their number to cover it.
The clearest way to prevent confusion in the first place, Marden says, is to set the terms before bids come in: state the expected project duration or ask each contractor to submit a timeline or schedule, and require a standardized, itemized form that breaks out insurance, taxes, and overhead and profit separately from trade costs and from project personnel and job site costs. Getting everyone on the same playing field before the numbers arrive is what actually makes an apples-to-apples comparison possible.
