Should we expect goods in identical packaging to have the same contents?
When communism collapsed in Central and Eastern Europe, previously unobtainable goods flooded the market.
Today, the region's shops and supermarkets offer broadly the same food and drink as in the West - a tangible and largely welcome result of global capitalism.
But something is dawning on Czechs, Slovaks, Poles and Hungarians: the labels might be the same, but the contents might not be.
In a German supermarket, Czech shopper Petr Zedinek holds up a can of tuna fish and leans in close, a conspiratorial gleam in his eye.
"A can of tuna fish," he says.
"Yes," I reply. I sense a larger point is coming.
"It costs €1." (78p; $1.09)
"In the Czech Republic it costs about €1.50."
"The fish here is good quality - whole chunks of it. Nothing like the mush they sell across the border."
Petr lobs several tins into one of the two shopping trolleys pushed by him and his 19-year-old daughter Klara. His wife Sarka is nearby. She looks for yoghurt.
Petr steers me to a large refrigerator full of smoked meats. He delves in and retrieves a plastic-wrapped package of sausages to show me the tiny writing on the back.
"Bockwurst. Look at the percentage of meat." I squint at the numbers: 87%.
"Try finding such sausages with 87% meat in a Czech supermarket," he says triumphantly, and tosses several packs into the trolley. I add one for myself.
We've driven - Petr, Sarka, Klara and I - about 20 minutes from their home in Modlany, a village close to Teplice. We've come to a small supermarket in the German town of Altenberg, just across the border in Saxony. They make the trip about three times a month. When we finish, the boot of Petr's new Skoda Octavia estate is full.
And it's not just Petr Zedinek and his family. About half the cars in the car park bear Czech licence plates.
Inside, the only language I hear is Czech; the only German-speaker is the cashier. In the 45 minutes we spend shopping, Petr bumps into one old schoolfriend and a Modlany neighbour.
"It does sound crazy, driving to another country to do your grocery shopping," says Sarka Zedinkova.
"But that's the way it is. And when you compare the products - identical packaging but something completely different hidden inside - I think it's a pretty sad state of affairs," she continues.
"Sometimes it seems to me that we're a kind of garbage can for the producers - what's left over, they send to the Czech Republic."
Under EU law, food companies can adapt their products to local tastes, even if the packaging is the same. In all cases the ingredients have to be clearly labelled.
But the Zedineks - and hundreds, probably thousands more families - have uncovered what they believe amounts to a conspiracy by some of Europe's food wholesalers.
It's not just a vague conviction that food in western Europe usually tastes better. They say identical products - sold in the same packaging under the same brand - are of much poorer quality in Central and Eastern Europe.
"Take this iced tea," says Czech Agriculture Minister Marian Jurecka, as he flicks through a PowerPoint presentation on his laptop, in an anteroom in the lower house of parliament.
The page shows the logo of the sickly-sweet, tea-flavoured drink sold in Europe's supermarkets and petrol stations.
"The packaging on the bottles is identical. So it looks the same in the Czech Republic and Germany. But the Czech one had 40% less natural tea extract," he explains, "and it was more expensive than the German one".
He clicks again.
"Or lunchmeat - the tin in Germany looks exactly the same as the Czech tin," the minister went on.
"But the one sold in Germany is made from pork, whereas the Czech one is reconstituted chicken."
The data is from a 2015 comparative study carried out by the University of Chemistry and Technology in Prague. Thirty students sniffed, prodded and tasted 24 products - coffee, cheese, margarine, chocolate etc - sold in identical packaging in Germany and the Czech Republic. The foods were then compared in the lab.
Eight of the products - 35% - were demonstrably different in either quality or composition.
Minister Jurecka is sceptical about the producers' claim to be catering for different regional tastes.
It may not be illegal to sell different food under identical packaging. But it is, he says, immoral.
So he and his colleagues from Slovakia and Hungary are gathering data to take to the European Commission. They want the law to be changed to force producers and distributors to stop the practice.
The issue has become a priority for the Visegrad group of Central European countries - the Czech Republic, Slovakia, Hungary and Poland.
Not everyone believes it worthy of so much attention. One Czech commentator complained recently that while leaders in western Europe were focusing their energies on resolving the Syria conflict, or tackling the migrant crisis, governments in Central Europe were fretting over the nut content of spreads.
So shouldn't politicians just ignore it and let the market decide?
"I guess the market is already deciding, with us driving across the border every week," says Petr Zedinek.
"But I think it's right the state should get involved. At least to some extent. To stop the customer being ripped off."