I work with contractors all the time on private and public projects. A lot of the time, especially on public projects, the change order is the result of nefarious intentions on the contractor's side to squeeze as much money as possible out of the owner because the government pays out big once a project is in the construction phase. CSI Format Specs were born out of the result of gross, shady contractors and increase project costs.

Lack of oversight leads to shit like this:

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• Public contracts go to the lowest bidder i.e. the lowest common denominator. So you're already off to a bad start.
• Contractor (bidder) intentionally bids as low as possible, hiring consultants to substitute as much equipment and materials as physically possible to decrease their bid. If you're lucky, sometimes they "accidentally" miss things in the contract and try to get a change order for those things later on, delaying construction.
• Contractor will go behind the designer/engineer/architect's back straight to the owner or your client, violating the chain of command set up in the contract mind you, and say "Hey I can do Z instead of X and save you (and the contractor themselves) $$$$!" Owner/Client then comes to you and is eager to move forward with this substitution or design change which puts pressure on you to approve an inferior product that may not work as good.
  • This usually leads to RFIs down the road from the contractor to the designers when something goes wrong with their substitution and throws their hands up saying "Well what should we do now??? You approved it!" even though the contract stipulates the contractor is responsible for added costs due to substitutions.
• Contractor has now spent a shit ton of money on consultants that was not part of their bid. They now need to make money on the contract and recoup the costs of the consultants.
• Contractor will continuously wear designers/architects/engineers down, sending in submittals that keep getting rejected for the same reason hoping they just relent. Sometimes they just give you submittals that have the completely wrong products for the spec or are just massively incomplete. They never send the full submittals if you do a partial approval.
• Contractor will submit products for review that don't meet the specs 99% of the time. Sometimes they change a minor detail that you can easily miss during review. Boom. They want a change order for the correct product. Nah sorry, you submitted a substitution. That's on you Mr. Contractor. Get bent.
• Contractors generally install things however they want, treating design drawings (the contract) as recommendations. Time after time I see contractors cut corners to save costs violating the contract. When these cuts get caught in inspections, it constantly delays construction.
  • Will submit products for approval, but not buy them and secretly substitute with something else.
  • Will not install equipment with proper clearances even though the design accounted for them. Here comes the RFIs, change orders, and inspection failures!
  • The worst contractor I saw was for a brand new HVAC system for a building.
    • He just reused the existing system, installed a few pieces of flexible ductwork, and put in some cheapo Home Depot fans (not powered or ducted) hoping he'd get away with it and call it a day. LOL. Lawsuit.
  • Will just not install items that allow for a complete, operational system.
• Change orders pour in as a result of a contractor's inexperience in installing projects of certain designs. They don't know how to do it so they think they deserve more money to figure out how.

I really could go on and on. Can I also say that CBRE is the worst consulting group I've ever worked with?