So I ran a little experiment to test how much of an impact the trade skill had on caravan profits. I deployed one companion with 100 trade skill and no tactics, and another with 80 tactics and no trade skill and tracked their daily revenue for 26 day. I gave both parties the same standard guards and did not modify their troops. What I found was that characters with high trade make more profits than those without. My spicevendor companion with 100 trade had an average revenue 196 higher than the falcon with no trade skill. That said on the 26th day I had to end the test because her caravan got destroyed by bandits.
A last point on all assigning your own troops to a caravan by finding them on the overland map and asking to inspect their troops. You can make make a Carvan much more resilient by assigning high tier troops, however, this will cut heavily into the caravan's profit margin though. All cavalry caravans will be much more survivable since they are able to avoid bandits and enemy armies, but that also means they will spend much more of their time running away from bandits than doing actual trading, which again cuts into your profits.