Why the same product costs different amounts at every merchant

Merchants publish product feeds on their own schedule. A price that updated forty minutes ago sits next to one that updated this morning, and that alone produces a visible gap.

Tax handling is the second cause. Some regions quote prices including VAT and some exclude it until checkout, so an apparently cheaper listing can end up more expensive at the final step.

Third, promotions are often merchant-funded rather than brand-funded. One retailer absorbing margin to win a category will undercut everyone else for a few weeks and then quietly revert.

This is why we show the last-updated timestamp on every offer and include shipping in the ranking. The cheapest headline price is frequently not the cheapest total.