Any "space opera" will have to have either (or both) of the following characteristics:
1. Much faster-than-light travel and communications.
2. Extremely robust social/political/economic institutions.Why? Simple. Planets are a long way apart; the closest likely habitable planets to us are 4+ light-years away, the second closest more like 13 l.y. For commercial purposes, there needs to be a way to finesse the extremely long time it would take for beings on Planet A to place an order with beings on Planet B and have that order delivered. With out closest possible neighbors, we're talking around 10 years, even with communications and travel at (or near) the speed of light. Transactions times in the decades are perhaps more plausible.
The alternative is, in effect, inter-planetary commerce that consists of "tramp spaceships" picking up loads of stuff on Planet X, heading off to the nearest planetary systems, and hoping to find a market (that seems to me to have been the Ferengi economic plan in Star Trek: Deep Space 9). And hoping that your customers will pay you in something that you find useful or can sell (barter) elsewhere. And being able to live with what you can get for sustenance. At the speed of light, you've got maybe 10 or 12 ports of call in your lifetime, assuming (a point Stross raises) you can keep your ship from falling apart, and/or can fend off space pirates. (Let's face it, piracy was a major problem for global commerce on this planet for hundreds of years.)
The alternative to all this is simply to hope your readers aren't paying enough attention, of just don't care.