Read the first five ingredients, which are most of the bottle. Decide whether you want a sulphate or not before comparing prices, since it changes how a shampoo behaves rather than how well it works. Conditioner belongs on the lengths, not the scalp. Serums vary: some are finishing products for the ends, used a few drops at a time, and some are made for the scalp — the label says which.
Sourcing, processing, label honesty, packaging and price all matter on this shelf. Read the back of the bottle for them instead of trusting a badge on the front.