Outdoor gear fails in ways that do not show in a photograph of it packed away.
Ask for it assembled
A tent pitched, a stove lit, a reel turned, a pack loaded. It takes a minute and it answers almost everything.
If a seller will not or cannot, treat the item as untested and bid accordingly.
Ask how it was stored
This is the question that separates usable gear from gear that looks fine. Packed away damp, left in a hot loft, kept in sunlight — all of them shorten a life invisibly.
"Was it ever packed away wet?" is worth asking about anything made of fabric. Mould does not come out.
Count the pieces
Poles, pegs, guy lines, inner, fly, footprint, stuff sacks, spares, fuel bottles, lids, straps. Ask for them laid out and counted on camera rather than described as "complete".
Age and service life
Waterproof coatings, elastic, foam and seals all have lives measured in years rather than uses. Ask how old it is, not just how much it has been used.
For optics
Ask to look through them on camera if possible, and ask about fungus, haze and whether the focus is smooth. Ask whether caps and a case are included.
What protection covers
Missing pieces described as present, undisclosed damage, mould that was not mentioned, or a different model than shown: not as described, seven days from delivery.
Honest wear that was described is not.
Questions people ask
Is a second-hand tent a good buy?
Often an excellent one, if it was stored dry. Ask that question before any other.
Does a leaking seam matter?
It is fixable and it is a discount. It should have been declared either way.
What about a stove that has not been used in years?
Ask for it lit. Seals harden with age and that is exactly what you are checking.