It can definitely be difficult to successfully transition those tiny plants, which usually have a rock-hard ball of peat in/around the roots, to a permanent home. Regardless of the type of store that sold it, if that's the condition of the plant, it's off to a bad start. When buying plants anywhere, inspect the roots. I couldn't agree more about preferring to patronize owner-operated stores! But don't automatically assume every plant at a BBS is incapable of living a long life. They often come from the same suppliers. Owner-operated does not necessarily mean anyone there propagates anything, but does usually mean the plants are much better tended while at the store. For that reason, it's much more likely to get a plant from an o-o store that hasn't been exposed to some kind of extreme that's actually common at BBS's (too dark, too sunny, too wet, too dry, too cold.)
There is no one ingredient one can put IN to make a better 'potting soil,' but one thing can be removed to do so. That thing is tiny particles, as Sewyn touched on. Tiny particles of anything - sand, silt, peat, clay, decomposing organic matter - lodge closely together, eliminating all tiny air spaces. While this is happening, roots also grow into the spaces, which is the path of least resistance AND where they find oxygen. Over time, this means that roots do not have access to oxygen. To combat, put whatever you want IN, except tiny particles of anything. Don't pack tightly in the pot, water gently the first few times to avoid mechanically compacting the mixture with the water. Over time the roots will fill the spaces again, the organic bits will decompose into smaller bits, so repeat as necessary.
Once you know the roots aren't rotting, your attention can turn to finding the best exposure, amount of light that your plants really enjoy. But sometimes a home or office environment, and/or locations outside where people put various plants can be so different from a plants' requirements that it can't do well. Other factors such as humidity levels, day length (latitude,) elevation, wind, rainfall, can apply (positively or negatively, depending on the particular plant,) in various locations.