Six Mercado Libre marketplaces put two currencies on one results page
In Uruguay, Paraguay, the Dominican Republic, Nicaragua, Guatemala and Panama the local currency and US dollars appear in the same list of results — which makes a per-country currency column quietly wrong.
Six of the seventeen Mercado Libre marketplaces — Uruguay, Paraguay, the Dominican Republic, Nicaragua, Guatemala and Panama — show local-currency prices and `US$` prices in the same results page. A dataset that attaches one currency per country is therefore correct in eleven markets and silently wrong in six, and the failure is invisible in the data: every row has a plausible number, and the aggregate is meaningless. Putting `currency` and `currency_symbol` on the row instead costs two columns and makes any sum, average or price index computable. The rule generalises beyond Mercado Libre: a currency belongs to a price, never to a country.
Key points
Uruguay, Paraguay, the Dominican Republic, Nicaragua, Guatemala and Panama show local and US dollar prices in the same results page.
A per-country currency column is correct in eleven of the seventeen marketplaces and silently wrong in six, with no visible symptom in the data.
Every row carries `currency` and `currency_symbol` as the page served them, which is what makes a sum or an average computable at all.
Mixing currencies is a fact about dollarised economies rather than a rendering quirk, so it will not be fixed by a parser change.
A currency belongs to a price rather than to a country, which is the rule that generalises past Mercado Libre to any dollarised market.
A bug with no symptom is the worst kind. This one produces a dataset where every row looks right and every aggregate is meaningless.
What the page actually shows
In Uruguay, Paraguay, the Dominican Republic, Nicaragua, Guatemala and Panama, a single Mercado Libre results page can list a price in the local currency and, two rows below it, a price in US$. Nothing in the layout separates them. They are simply two sellers who chose different units.
Why six markets and not all of them
Because those six economies are partly dollarised, and the marketplace reflects that rather than normalising it. Argentina and Mexico price in one currency, which is exactly what makes the bug hard to catch: it does not appear in the markets most people test in first.
The failure mode, which has no symptom
Attach one currency per country and nothing breaks. Every row holds a plausible number. The dataset validates. And then a sum, an average or a price index over a mixed-currency market adds guaraníes to dollars and returns a figure that means nothing at all — with no error, no null and no outlier to notice.
Putting the currency on the row
currency and currency_symbol come back on every row exactly as the page served them. Two columns, and any aggregation becomes computable — group by currency, or convert using a rate you chose, but at least the choice is now yours to make.
Where else this rule applies
Venezuela takes it further: product pages there carry both currencies for the same item, which makes the exchange rate itself observable. And the same instinct — store what was served, not what you assumed — is why sales figures stay as text.
Frequently asked questions
▸Which Mercado Libre countries mix currencies?
Uruguay, Paraguay, the Dominican Republic, Nicaragua, Guatemala and Panama. In those six, a single results page can contain prices in the local currency and prices in US dollars, side by side and with no separation in the layout.
▸Why is a per-country currency column dangerous?
Because it fails silently. Every row still holds a plausible number and nothing in the dataset looks broken, but a sum or an average over a mixed-currency market combines two different units and produces a figure that means nothing.
▸Does this affect Argentina or Mexico?
No. The large marketplaces price in one currency, so a per-country column happens to be correct there. That is exactly what makes the bug hard to catch: it works in the markets most people test in first.
Sources
Every URL below was requested and returned a page on the date shown.
A working method for extracting listings and product pages from any of the 17 Mercado Libre marketplaces, including the two decisions — pagination and detail pages — that decide what a run costs.
Mercado Libre results mix `articulo.…/MLA-…`, `/p/MLA…` and `/up/MLAU…` links. Deriving the item id from the URL looks fine until the third shape appears, which can be nearly half a page.
A reference table of every Mercado Libre site id, its country, its currency, the depth of a single query and whether it has catalog pages, mixed currencies and installments.
