Second-hand construction sets move quickly, which tempts people to photograph a heap of parts on a carpet and write a one-line description. That listing will sell, and then it will generate a complaint, because the buyer expected a set and received a bag. Ten minutes of preparation makes the difference between a clean sale and an argument about a refund.
Sort before you photograph
Lay the parts out by type: connectors grouped by number of ways, rods grouped by length, wheels and gears separate. A sorted photograph tells a buyer what they are getting far better than any word count. It also tells you what you have, which you need before writing a single line of the description.
Say plainly whether it is complete
Almost no used set is complete, and buyers know this. What they need is an honest statement: original box with booklet, contents not verified against the parts list. That sentence is accurate, sets expectations and protects you. Claiming completeness for a set assembled from three boxes is where disputes come from, because instruction sheets in ranges like K'NEX assume one exact parts list and stop working when a connector is missing.
Condition matters more than age
Plastic that has lived indoors at room temperature can be twenty years old and fine. Plastic from a garage or a sunny conservatory can be five years old and unusable: brittle rods, faded colours, connectors that no longer grip. Flex a few rods before listing. If they snap rather than bend, you are selling craft material, and you should say so and price it accordingly.
What to include in the listing
- Photographs of the sorted parts, not a pile.
- Whether the box and booklets are present.
- An approximate part count and how you arrived at it.
- A clear note on any powered components and whether they were tested.
- Any damage, discolouration or previous storage in a garage or loft.
Batteries and powered parts
Remove every cell before packing, including coin cells, and dispose of them properly rather than posting them. Beyond the postal rules, a loose coin cell arriving in a box destined for a child's room is a genuine hazard, because swallowing one can cause serious internal injury within hours. If a motor was working when you last used it, say so in those terms rather than guaranteeing it.
Packing so it arrives usable
Bag by part type rather than tipping everything into one sack, and the buyer will thank you in feedback. Double-bag anything sharp-ended, and pad the box, because thin rods survive a fall better than they survive being crushed under a heavier parcel. Include the booklets flat rather than folded around the parts.
Giving it away instead
Charity shops, nurseries above the age line and school clubs all take these sets, but they will not sort them for you and some are already full. Ring ahead, sort it anyway, and be honest about missing pieces. A donation that arrives clean, bagged by type and clearly described gets used; one that arrives as a carrier bag of mixed plastic quietly goes in a skip.