Some things should not go in a van. A tall vase. A framed textile. Twenty laddoos. A cake.
When a seller marks an item collect-only, it means exactly that: it will not be posted, and winning it means coming to get it.
You agree before you bid, not at checkout
This is the part worth understanding properly.
The terms are shown to you before the bid, because the time to find out an item cannot be posted is before you have won it — not at a checkout screen when you are already committed.
What you are shown: where, and how long you have.
How long you have
72 hours from the moment the seller marks it ready, by default.
A seller can set it shorter or longer — six hours at the least, two weeks at the most — because fresh flowers and a stoneware plate are not the same promise. Whatever they chose is on the listing.
If you never come
The store keeps 7% and the rest is refunded to you.
A seller can set that as high as 20% and no higher. For something that spoils while it waits — food, flowers, anything with a life — it is a flat 20%.
That is not a penalty for changing your mind. It is somebody who stopped working, wrapped a thing, and kept it on a shelf for three days.
Why this exists at all
Because the alternative was sellers not listing those items. For a long time the only options online were "pay for shipping" or "do not sell it", and a great deal of the best work quietly fell into the second category. The longer argument.
Collecting
Bring something that identifies you as the buyer. Check the item before you leave — you are standing in front of the person who made or sold it, which is the one moment when a question is easiest to answer.
If you are going somewhere you have not been, go in daylight and tell somebody where you are.
Questions people ask
Where exactly do I collect from?
The area is shown before you bid; the full address once you have paid.
How long do I have?
72 hours by default, from when the seller marks it ready. The listing states the actual figure.
What if I am late?
Talk to the seller. They can often be flexible; they are not obliged to be.
What happens if I never collect it?
The store keeps 7% by default — up to 20% if they set it higher, and a flat 20% for anything that spoils. The rest is refunded.
Can somebody else collect for me?
Usually, if you arrange it with the seller first.
Can I inspect it before paying?
Payment happens when you win, before collection. If it is not as described when you get there, raise it.
Can I ask for it to be posted instead?
Only if the seller offers posting on that item. Many cannot.
Next: how delivery is charged, or the quiet case for meeting in person.