Second-hand suits Cottage Goth unusually well because the aesthetic already values wear, useful objects, natural fibres and clothing that looks collected over time.
The mistake is searching only for “Cottage Goth”. Sellers may never use the term, and the most useful pieces often pre-date it by decades.
Search for material and cut
Try black linen dress, wool maxi skirt, velvet jacket, Donegal cardigan, corduroy trousers, lace collar blouse, leather lace-up boots, wax jacket or long wool coat.
Those searches describe the thing itself. Add size, colour and measurements to narrow them.
Measurements matter more than the label
Vintage sizing is inconsistent and modern brands vary widely. Ask for pit-to-pit, waist, hip, shoulder, sleeve and total length where relevant.
Compare those figures with a garment you already own and like. This is more reliable than guessing from S, M or a historical size label.
Charity shops reward a broad eye
Look through menswear for wool coats, knitwear, shirts and leather belts. Check occasionwear for velvet, long skirts and old jackets. Home sections can turn up brooches, scarves and bags alongside the clothes rails.
A garment can be wrong in isolation but right as a layer.

Natural fibres deserve attention, not worship
Wool, linen and cotton age beautifully, but a good viscose dress or mixed-fibre coat can still be useful. Check condition, care requirements and how the fabric feels rather than treating fibre content as a moral score.
Moth damage matters in wool. Hold pieces up to the light and inspect folds, cuffs and underarms.
Learn three simple repairs
Replacing a button, closing a loose seam and basic darning will rescue a surprising amount of clothing. Hemming trousers or skirts can turn an almost-right find into a favourite.
For structural alterations, use a tailor rather than sacrificing a good garment to optimism.

Shoes need more caution
Used leather boots can be excellent if the sole, heel and upper remain sound. Check internal wear, cracking and whether the previous owner's foot shape has distorted them.
A cobbler can replace soles and heels, but not every cheap pair is worth rebuilding.

Build combinations, not a haul
Before buying, ask what the item works with already. A black skirt that pairs with three shirts and two knits is more valuable than a spectacular garment that needs an entirely new supporting cast.
Photograph useful combinations on your phone. It makes gaps obvious and reduces duplicate buying.