Why this keeps happening
Common names were assigned locally, over centuries, by people who had no reason to coordinate. Botanical names were assigned later by people who did. Where a trade crosses a language boundary the common name usually survives and the plant underneath it changes, and nobody involved is being dishonest — the label is simply carrying less information than the buyer assumes.
The two marigolds
Calendula officinalis is the orange pot marigold of European blends: colour, almost no flavour. Tagetes lucida is the Mexican marigold: strongly aniseed, and drunk as pericón. Both are called marigold in English and they are different genera. Buying by the English name across that boundary gets the wrong plant.
The two verbenas
Lemon verbena is Aloysia citrodora, a South American shrub, and is what a French café means by verveine. Vervain is Verbena officinalis, a bitter European wayside plant with no citrus character whatever. They share a family and nothing a drinker would notice, and the substitution runs in both directions constantly.
The two cinnamons
Ceylon cinnamon is thin, layered and crumbles between the fingers. Cassia is one thick hard curl that does not. Outside Britain, Mexico and Sri Lanka, the word cinnamon on a packet almost always means cassia, and a recipe written in one convention read in the other produces a different result.
The things sold as something more expensive
Safflower has been the saffron adulterant for a thousand years; safflower florets are flat and tongue-shaped, saffron is a trumpet-shaped stigma, and the price gap is roughly a thousandfold. Snow chrysanthemum is a Coreopsis. Carob is sold as a cocoa substitute and shares neither the fat nor the bitterness that make cocoa taste of cocoa.
The check that works
Look for the binomial. A seller who prints Aloysia citrodora is telling you something; a seller who prints 'verbena' is not — usually through habit rather than intent. Where TeaHQ records a botanical name it is because that name is settled, and where it omits one it is because it is contested.