A price came back as one number with no build-up
Nobody can see what has been missed, so the trade who priced it blind either comes back for more money or cuts corners to make it work.
What's happening?
A lump sum with no breakdown is a price you cannot interrogate. Whether the steelwork allowance is generous or missing, whether attendances are in, whether the temporary works were understood - none of it can be seen, so the comparison collapses to cheapest wins and the risk stays hidden until the job makes it visible.
It lands badly either way. If the number is light, the subcontractor discovers it mid-job and the shortfall comes back as claims, corner-cutting or a walk-off; if it is heavy, you paid for risk that one round of questions could have taken out. The fix sits at enquiry stage: a breakdown required with the tender, and the returns analysed against scope before anything is signed.
The solution
Prices you can see inside before you commit to one.