Testing as a homeowner is leisurely. You place a device, you keep the house closed, you read the result whenever it comes and you decide at your own pace. Testing during a sale has none of that slack. The test has to be placed, run and reported inside an inspection window, and the result lands in front of two parties who want different things from it.
That does not make it complicated, but it does make sequencing matter. The failure mode is almost never a technical one. It is a test placed with barely enough time to run, a result arriving on the last day of a response window, and both sides negotiating a construction question they have not had a chance to think about. Raising radon at the start of inspections avoids nearly all of that.
Most commonly the buyer arranges radon testing as part of inspections and pays for it, the same way other inspections are handled. Sellers sometimes test before listing instead, which lets them handle any result on their own schedule and present the paperwork with the disclosure package. Both approaches are normal, and the important thing is that everyone knows which one is happening. Agents usually have a preference based on how transactions in the area tend to run, which is worth asking about before inspections are scheduled rather than after.
Get the specifics in writing early: who orders the test, who pays, which contractor is placing it, when it goes in, and who receives the report. In a transaction the report is a document both sides will read and refer back to, so it should come from the contractor to the agreed recipients rather than being relayed secondhand. Keep the raw report, not just a summary of the number.
A test needs its full run and the result needs time to arrive, and both of those have to fit before the deadline for responding to inspection findings. Working backward from that deadline is the whole scheduling exercise. A device placed late is the most common way a radon question turns into an extension request. If a holiday, a long weekend or a lab turnaround falls inside that window, count it in when you choose the placement date rather than discovering it later.
Access is the other half. The house must stay closed up for the duration, which is awkward when showings continue, a seller is packing, or a tenant is living there. Everyone with a key needs to know the test is running before it starts and needs to know not to move the device. This is why continuous monitors are common in transactions: their hourly logs show whether conditions actually held, which turns a potential argument into a readable record.
A result at or above the action level the EPA publishes is not a deal-breaker and should not be treated as one. It is a known condition with a standard remedy, and the remedy is a routine installation rather than a structural repair. The useful next step is a quote for sub-slab depressurization, so the conversation is about a defined scope of work instead of an open-ended worry.
From there the parties negotiate the same way they would over anything else found during inspections. The seller mitigates before closing, the buyer takes a credit and handles it after possession, or the cost is split. Whichever path is chosen, insist that a post-installation test be part of it. The thing a buyer actually wants at closing is a confirming measurement, not a receipt. Ask who arranges that confirming test and who receives the report, because a system installed in the final week before closing leaves very little room for it.
An existing mitigation system is a positive, not a red flag. It means somebody tested, found a number that warranted action, and fixed it. What you want to establish is whether it still works. Ask when it was installed and by whom, whether there is a post-installation test result, roughly how old the fan is, and what the gauge on the pipe reads right now.
Then test anyway. A fresh measurement tells you what the house is doing today, which is the only thing that matters at closing, and it establishes a baseline for your ownership. Ask for the installation paperwork to come with the house, and put the fan's approximate age on your own maintenance list, since fans wear out and a stopped one gives no indoor sign at all.
In practice they are handled like other inspection findings and are commonly negotiated. Typical outcomes are the seller arranging mitigation before closing, a credit to the buyer who handles it afterward, or a split. What matters more than who pays is that a post-installation test is included, so whoever ends up owning the house owns a verified system rather than an unverified installation.
Treat an older result as background rather than as a current answer. Levels move with season and weather, and how a house is operated changes with its occupants, so a reading from a previous owner's routine may not describe yours. An older test is useful context, especially alongside a mitigation system's paperwork, but a fresh test is what tells you where the house stands now.
That is a conversation for you and your agent, since access is a contractual matter rather than a technical one. What you should not do is treat the refusal as an answer either way, because it tells you nothing about the house. If a test cannot be run before closing, plan to test promptly after possession and budget for the possibility that mitigation is warranted.
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