A six-year-old tent kept dry indoors is worth more than a two-year-old one packed away wet. That sentence is most of this category.
What moves the number
Whether it still does its job, demonstrated.
How it was stored, which is the question nobody thinks to ask and everybody should.
Completeness — poles, pegs, guy lines, inner, fly, stuff sacks, spares.
Service life — coatings, elastic, foam and seals age whether or not the item was used.
Brand, where it carries a reputation for lasting.
Why two of the same differ
One seller pitched it on camera and said it had been stored dry indoors. The other photographed a stuff sack. Describing outdoor gear.
How to find out rather than guess
Compare completed sales of the same model in a stated condition, and discount hard for anything untested or stored badly.
Mould is not a cosmetic issue and does not come out of fabric. A mouldy item is a parts item.
What is worth more than people expect
Complete older gear from makers with a reputation, optics in good order, and anything that has been genuinely looked after and can be shown working.
Questions people ask
Does re-waterproofing raise the price?
A little, if you say you did it and with what. Many buyers would rather do it themselves.
Is a missing peg a real deduction?
Only if you hide it. Say it and it is nothing.
What about old stoves?
Ask for them lit — seals harden with age, and that is the whole question.
More: pricing outdoor gear, packing it.