What are the biggest red flags when hiring a plumber?

Plumbing red flags cluster around two patterns: scope inflation (turning a fitting repair into a whole-home repipe) and unlicensed work (water heater, gas line, drain reroute). The downsides are slow leaks behind walls, gas leaks, mold, and insurance denial when unpermitted work fails.

Whole-home repipe pitched off a single failed fitting. The plumber arrives to fix a slab leak or a single corroded coupling and announces that "all your pipes are corroded" and the whole house needs to be repiped in PEX or copper. Sometimes that's true (Kitec, Quest Pb, certain galvanized eras), but it requires evidence — visible corrosion at multiple sample points, water quality test, plumbing age and material documentation. "Trust me, I've seen this before" is not evidence. Get a second quote before approving anything over $5,000.

No permit on water heater, gas line, or drain reroute. Water heater replacement requires a permit in nearly every jurisdiction (gas, venting, T&P relief, expansion tank, seismic strap). Gas line work always requires a permit. Drain reroutes that change the venting or trap arm require permits. A plumber who proposes to skip the permit because "it's just a swap" is shifting permit-fail and insurance-claim-denial risk to you. Walk away.

Missing Master Plumber license or specialty-only license. Verify the license matches the work — a gas-only specialty license cannot legally perform water-supply or drainage work. Verify the qualifying party name matches the person on site. A C-36 license (California), Master Plumber (Texas), CFC (Florida), or equivalent is the minimum for permitted work.

Pre-emptive whole-home water shutoff during quoting. The plumber shuts off the main and refuses to turn it back on until you sign a contract for emergency work. This is leverage extraction. A real plumber turns the water back on and gives you a written estimate to consider overnight.

Cash only, large upfront deposit. Any deposit above 10-15% upfront, demanded in cash, is preparing-to-disappear behavior. California caps deposits at 10% or $1,000 for licensed contractors.

"Your sewer line needs a full replacement" without a camera scope. Sewer-line full replacements are $5,000-$25,000 jobs. Any quote for a full replacement must be backed by a video scope you can watch — and ideally a second opinion from a different plumber with their own camera. The clay-pipe-needs-replacing pitch is one of the most common high-dollar plumbing scams.

"Your hot water heater is about to fail." Sometimes true (over 12 years old, leaking, sediment evidence), often manufactured. Ask for the age (date plate on side of unit), the failure indicator (drip pan rust, T&P discharge history, sediment flush result), and the manufacturer warranty status. A water heater with 6 years of life and no leaks is not "about to fail."

No itemized estimate. "It's about $X" is not a quote. Real estimates separate labor hours, fixtures (by manufacturer/model), and consumables.

Groundcheck (earthmove.io/trust) verifies the plumber's state license, surfaces prior citations and complaints, and detects phoenix-company patterns. It does not verify the technical accuracy of a specific diagnosis — second-quote any job over $5,000.