Should I try a used car seat in my car before I pay?

Why do RoSPA and NHS say try it in the car?

RoSPA's before-you-accept list is blunt: try the seat in your car — if you cannot get it to fit securely, do not buy it. Which? repeats the same line and adds any other car you will use, including a grandparent's. NHS and local NHS pages tell you to test a seat in the car and to avoid second-hand seats whose history you do not know.

Good Egg's used-seat tips (as published on their buying-tips page) add a step before you even travel: some makers publish fitting lists or online fit finders. They also flag car-specific snags such as buckle crunch, floor storage boxes and awkward Isofix anchor points. A porch pickup skips every one of those checks.

A fit check answers one question only: does this seat lock into this car, this week, using the instructions? It does not tell you whether the seat was in a collision. Official pages treat those as separate problems.

What should I prepare before I drive to the seller?

• The car the child will travel in — not a friend's lift. You need that Isofix geometry and that seat-belt buckle.
• The official instructions for that model — download the PDF if the listing has a readable model name. Fitting from memory is not RoSPA's "instructions available".
• The maker's vehicle list, if they publish one — Isofix seats are often approved only for named cars. Good Egg tells you to check that list.
• Time and daylight — you need to see indicators, belt routes and whether the seat rocks.
• Agreement in writing that you will fit before you pay — if they will only do a porch handover, you cannot run this page.

How do I run the Isofix click or the belt route on the drive?

Use the model's own instructions. The steps below are the collection-day order, not a substitute for the booklet.

1. 1
   Clear the adult seat Move the front seat, buckle and any under-floor lid so you can see the Isofix anchors or the full belt. Good Egg flags floor storage boxes and buckle position as common reasons a "yes" on a fit list still fails in the metal.
2. 2
   Isofix route (if the seat uses it) Extend the arms, align with the car's Isofix points, and push until you get the click the manual describes. Many seats then show a green indicator. If an arm will not lock, or one side is green and the other is not, the fit has failed. Do not force a second-hand arm that feels gritty or bent.
3. 3
   Support leg or top tether If the PDF requires a support leg, it must sit on the vehicle floor the manual allows — not on a flimsy storage lid unless the maker says that lid is approved. If the PDF requires a top tether, find the car's tether anchor and tension it as drawn. Missing hardware is a failed fit, not a later purchase.
4. 4
   Belt route (if the seat uses the car's seat belt) Thread the belt through the colour-coded path in the instructions. Lock the belt as the booklet says. The buckle should not sit on the belt path (the "buckle crunch" Good Egg names). If the belt will not stay tight, or the seat slides on the bench, do not pay.
5. 5
   The wobble check the booklet describes Follow the maker's test for movement at the belt path or Isofix bight. If the instructions say the seat must not move more than a stated amount, use that. If you cannot get it stable, RoSPA's line is do not buy it.
6. 6
   Repeat in the other household cars Which? says include a grandparent's car. A seat that clicks in yours can fail in a smaller city car or a different Isofix spacing. Do that before money changes hands if those cars will actually carry the child.

If it clicks, have I cleared the crash-history problem?

No. RoSPA, GOV.UK and the Lullaby Trust all say crash damage may not be visible. A green Isofix window only shows the connectors engaged today. Good Egg's own clinic wording (on their used-seat tips) is that they can confirm whether a seat is fitted and used correctly; they cannot confirm the seat is sound without knowing the history.

The seller will not let me bring the car. What then?

Then you cannot run RoSPA's try-in-car step. A photo of the seat in their car shows their car, not yours. Posted parcels and porch pickups are the same block. Official advice is not to buy a second-hand seat online in the first place; a seller who refuses a fit is not offering the one check those pages still ask for if you go ahead.

In shortBring the car. Fit Isofix to a click or run the belt path from the PDF. Repeat in a grandparent's car if they will drive. If it will not sit securely, RoSPA says do not buy it. A perfect click is still not a crash-history pass.

Should I get the fit checked again after I pay?

If you did take the seat, RoSPA still points you at the instructions and a secure install. Good Egg and some council road-safety teams run checking clinics. Use them to confirm the install in your cars. They will not — and Good Egg says they cannot — certify an unknown past.