Formats and concentration
What is a perfume decant
A perfume decant is fragrance transferred from its original container into another container, usually in a smaller quantity. The seller, source fragrance and transfer process matter; a decant is not automatically an official brand sample.
A HUME Fragrance buying guide

Identify the original fragrance
Check the full name, brand and version claimed by the seller. Familiar labels on a small atomizer are not independent proof of provenance.
Distinguish sample types
A manufacturer's sample, a third-party decant and an inspired fragrance are different products. They can all be small, which does not make their identities interchangeable.
Review seller information
Read quantity, packaging and purchase conditions carefully. Keep the exact name in your notes so a later full-bottle order matches what you intended to test.
Try this before you buy
Write whether each small-format listing is a brand sample, third-party decant or inspired fragrance before comparing prices.