A contractor quote can go up after work starts, but the increase should be tied to newly discovered conditions or approved scope changes rather than vague surprises.
When price changes are legitimate
Hidden deck damage, concealed plumbing failures, unsafe wiring, and broader moisture spread are examples of real discoveries that can change scope mid-job. That is especially common on roof repair, plumbing repair, and water damage projects.
What should happen before the price changes
The contractor should explain what changed, document it, price the added work, and get your approval before continuing whenever possible. If the original quote was vague, compare it with what a complete estimate should include to see whether the risk was disclosed from the start.
How to protect yourself before work begins
Ask how hidden conditions are billed, what common change-order triggers the contractor expects, and how approvals will be handled. The cleaner the original scope, the less room there is for confusion later.