Business owners in Phoenix who send identical construction plans to five contractors often receive five bids that appear to describe entirely different buildings. According to Mike Marden, a registered architect, licensed general contractor, and founder of WDS, a Phoenix-based integrated design-build firm, the spread rarely reflects contractors trying to take advantage of owners. Instead, it usually traces to project fit and the wide room for interpretation built into the bidding process itself.
The stakes are significant for anyone planning commercial work, because an owner who selects a bid without understanding what it actually covers can face unexpected costs, incomplete scopes, or supervision gaps once construction begins. Marden, who has observed the bidding process from both sides of the table for decades, says the variance almost always comes back to a handful of specific gaps, and that knowing them makes comparing bids far easier.
The first issue is what contractors are actually looking at. If a bid is based on a preliminary walkthrough rather than a finished, detailed set of plans, Marden says there is already 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 the next contractor's experience, and that alone can start the variation. Even with a full, specific set of plans, numbers can diverge based on how much time and attention a contractor plans to devote to the project, a difference that shows up directly in the final price through supervision, management, and overhead.
Missing scope causes even bigger gaps. One of the most common reasons bids spread apart, according to Marden, is that some contractors examine 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.
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. He recommends asking bidders to break their numbers into separate scopes, because without that breakdown, markups such as overhead, insurance, and taxes stay hidden inside a single lump-sum figure. For larger projects, he suggests separating a project into logical phases first, such as interior work versus site work or landlord work versus tenant work, then breaking out each trade individually. Every bidder should also detail supervision costs specifically, since Marden considers supervision one of the biggest drivers of price differences; some contractors provide a daily on-site quality control supervisor, while others may simply have someone occasionally drive by the job site.
Marden also warns that a bid looking too good to be true often is. He advises checking whether the contractor has completed the same type of project before, noting that a company skilled at building houses is not automatically qualified to build a medical office or restaurant, and suggesting owners review the kinds of projects photographed on a contractor's website. 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 the number to cover it. The clearest prevention, Marden says, is to set terms before bids arrive: state the expected project duration or require each contractor to submit a timeline, and require a standardized, itemized form that separates insurance, taxes, and overhead and profit from trade costs and from project personnel and job site costs.
