The thing nobody talks about with clear pots is how much the light changes root behavior. Roots are not supposed to see light, so when you put them in clear plastic the ones touching the sides can turn green and even grow algae on them. I ran a few of my plants in clear orchid pots for a year and the roots near the edge got this green tint, which is actual chlorophyll forming. It did not kill the plants but it slowed them down compared to the same plants in dark pots. My fix was sliding the clear pot inside a slightly bigger clay pot and only pulling it out to look every couple weeks. You still get to watch the roots but they get their dark back in between checks.

Did you save that guy from a real mess or what? It's easy to laugh at rookies but we've all been there, and nobody wants to be the one scrubbing black soot off a customer's floor for free. Good on you for speaking up instead of just letting him learn the hard way.