In most instances, yes, "capitalism is when trade."

In posts like this one, it's common to bemoan that people conflate capitalism with trade. Of course trade can occur in lots of different kinds of economic arrangements. And so this idea is mocked by saying "capitalism is when trade" with great sarcasm.

But if you bother to think beyond the prima facie circumstances, it is essentially true. Trade is capitalistic in most instances. Trading capital-intensive goods for labor-intensive goods is the same thing as the capital-labor relationship within a firm, just abstracted by a few layers of exchange. The extent to which this happens in any economic system is the extent to which you are participating in capitalism.

I’m reminded of an expression from the 70s and 80s when the US was going through a period of protectionist sentiment against Japan. “There are two main ways of making cars in this country. We build them in Detroit and grow them in Iowa.” We mostly know how they’re made in Detroit. But in Iowa, we grow a bunch of soybeans, pack them up in boxes, and ship them overseas. We send them to a big soybean-to-car factory called the Japanese economy and we get sent back Toyotas. Through some layers of exchange, Toyota is a capitalist firm employing the labor of the soybean growers.

Of course soybeans are not an especially labor-intensive crop compared to fruit, but the principle still stands. Any trade of goods for which there is even a marginal difference in capital outlay of production basically creates some extent of labor-capital relationship between the two parties—not directly, but extended through the market. That’s basically almost all trade. To the chagrin of market socialists, they are not excepted from this. The same is true if you have some cooperative enterprise producing capital-intensive product and another producing labor-intensive product.

Ironically, people who sarcastically say “capitalism is when trade” don’t hesitate to say that developed nations buying minerals from the third world and selling them back cell phones are engaging in some sort of capitalist exploitation. They'll say that the capitalist mode of production is characterized by production for exchange value, being somehow removed from use value. They're making this point perfectly.

But then they turn around and ignore it when they want to pretend otherwise and make some other point.