The single most useful habit in this category costs you nothing: measure a garment you already own and like, and keep the numbers on your phone.
Ask for the numbers
"Can you measure the chest flat?" and whatever else matters for the garment — inseam, shoulder, length. Ask for the tape on camera.
A seller who measures without being asked has sold clothes before. A seller who says "it's a medium" has told you very little.
Compare against something real
Your own well-fitting shirt, measured flat, is a better guide than any size chart. Two centimetres across the chest is noticeable; five is a different garment.
Ask about alterations
A garment that has been taken in or hemmed does not match its label. It is not a fault — it is a fact that changes what the measurements mean.
Then the condition questions
- Cuffs, collar and hems — where wear shows first
- Pilling, under the arms and on the inside of sleeves
- Fading, especially on dark cotton
- Stains, holes, repairs — where and how big
- Smell
On brands
Nobody can authenticate a garment over a video call. Ask what the piece carries and where the seller got it. A careful "I bought it second-hand and cannot confirm more" is worth more than a confident assurance, and should be priced as what it is.
What protection covers
Measurements that are materially wrong, undisclosed damage, an alteration that was not mentioned, or a different garment than shown: not as described, seven days from delivery.
A garment that fits differently than you hoped, when the measurements were accurate, is not. That is why the numbers matter.
Questions people ask
What if the seller will not measure?
Bid as though you had no size information, or do not bid. This is the one request worth insisting on.
Does pilling come off?
Some, with care. Assume it does not when you decide your number.
Is second-hand clothing hygienic?
Wash it on arrival, following the care label. Sellers should say whether a garment has been washed. How returns work.