I changed commerce to a structure in my game files because it is not useful enough to be an industry.
This, right here, is supertruth.
Commerce is in no way worth an industry slot. It's useful, but it's not
that useful.
It's a trash-to-money converter. And another source of supplies, fuel, and crew. The extra stability is incedental.
Also for those wondering, you pay a tariff when using the commerce market on your planet because it is not your market.
It belongs to the independants. And as such allows you to increase your indy reputation by buying/selling stuff there, if that's a thing you ever need.
And you don't get a black market because that would remove basically all the risk associated with getting to/dealing with one.