Samples
A sample is a small vial produced by the brand, usually 1 to 2ml, and usually free from a counter in a department store. It is the most authentic option because it comes from the manufacturer, but it is also the least convenient — you cannot buy one for a fragrance that is not in a shop near you, and the vial will not last long once opened.
If you have a department store nearby with a fragrance counter, this is free and it costs you nothing but the visit. It is genuinely the best way to narrow a list of ten fragrances down to two or three.
Travel sprays
A travel spray is an original manufacturer format, usually 5 to 15ml, designed to be carried. This is the most straightforward option to buy online because the brand makes it, so what you receive is what the label says.
The is a clear example of a full manufacturer travel format. The trade-off is price per millilitre — you are paying a premium over the equivalent volume of a decant because you are buying the branded packaging and the retailer's margin.
Decants
A decant is fragrance poured from a full bottle into a smaller container by a reseller. This is where the value is: you get genuine perfume at a genuinely lower cost per millilitre, because you are not buying the bottle and the box.
A and a are typical of what is available, and the per-millilitre economics are considerably better than buying two or three full bottles to find one you like.
Sample lots and selections
Lots are the format that requires the most care, because what you receive is not individually specified. A or a can be excellent value if the seller is reliable, and a poor use of money if they are not.
Before buying a lot, check the listing carefully for which fragrances are included. A good seller names them. A seller who will not name them is telling you something.