That is one way to handle it, and might be a good approach. My usual method is to make it clear that a 'Speculative Trade' (singular) is the result of a week worth of work from the entire crew; filling the hold with freight is pretty easy in comparison. A 'Speculative Trade' often comes with an adventure attached, too -- this is not 'business as usual' it is a reward for doing extraordinary things.
So here's the thing with the speculative trade system. It is *supposed* to be an adventure prompt, not an end result in and of itself. Traveller has never done a good job of explaining this in the actual rules, so large numbers of people think it's a complete system. But it is an adventure prompt, just like all the other RNG elements of CT such as patrons, random encounters, law enforcement hassle checks, and so on. This is why the system does not have rules for rival merchants, corrupt dealers, obnoxious custom agents, tariffs, or any of the rest. The GM is supposed to take the prompts and make stories out of. Not necessarily every single trade, some do just work.
But if you look at the CT merchant adventures, they are never just rolling for a thing and selling the thing later. Look at the Traveller adventure and the various amber zones: You stop at the planet and the best deal is on the local wine, but there's a big corporation trying to corner the market, so you go into the hinterland to bypass them. Or you go to the planet and it has rare wood, but you have to go into the small towns to get any that's for sale to rando tramp traders. You go there to sell medical supplies and there's a rebellion trying to destroy the supplies. You run food to this other place, but someone forgot to mention that the best buyers are criminal organizations.
The Traveller speculative trade system requires the players to be actively incompetent AND roll badly to lose money. The idea is that enough of the trades go smoothly so the ship stays flying, but many of them have significant complications that result in stories.
That's not trampling on players' chosen skills. That's putting their skills to use and playing the game, which is being adventurers. John Falkayn and Nicholas Van Rijn go on all manner of adventures where trade is the WHY, but it is not the WHAT that they are doing. And that's what Traveller was trying to replicate.