This is why the low and high bid are automatically thrown out, and then the remaining bidders are investigated for ability to actually deliver. For real world contracts change orders are where the real money is - that is places where your specification is wrong for some reason not known in advance and you will need to pay for the fix. The low bidders are experts in figuring out how meet the letter of the specs while building something that doesn't make sense (By spec the toilet drains pipes won't connect to the toilet, we can fix that for only $$$). A more reasonable contractor will see that and make the obvious fixes while for no extra charge, but not the low bidder - this makes the low bidder more expensive.