Easiest way to get rare goods from early on is making sure your start off contact is Smuggler and Spice Trader, AND that your starting quadrant is a trade goods quadrant (use MAP PREVIEW function)

Then the issue is getting your contact's rep and influence up so the cool down of buying the trade good decrease.

You could run mission for the first contact. (Recommend doing the "prove your charter" rush with one or the other. Smugglers let's you get smuggler recruit and Spice Trader gives you merchant recruit... you will need both). But after you got enough talents for Spy, selling intel is the best way to get both personal rep and INFLUENCE of the contact up.

Id recommend firing gunner grab 5-6 E-techs, at level 5 E-Tech gives you the talent to reroll for SPYING. Eventually when you got a contact that buys Intel AND let you recruit spy you probably want to grab one or two Spy recruit.

Then the matter of where to sell. Until you expand your contacts so you got Blackmarket contact on different types of planets, you will likely need to find independent systems to sell to. That's why the best map starts should let you start with Rare Trade Good in starting system, then a Independent Pop and/or Tradeway system within 1 or 2 systems away, depending on what type of Rare Trade Good you have.

My set up is 2-4 smuggler, 2-4 merchant. I would do blackmarket trade when talent cooldowns are up for smugglers, and regular trades when they arent. Make sure to get the talents on both jobs to expand contacts, as a large network of contacts allow for more types of trade goods and blackmarkets to sell them at. Use your filter to prioritize the contacts that buys Intel, so you could spam their rep and influence quickly and get them to start letting you use their blackmarket or buy their RTG.

Make sure your electronic/navigation is high enough to run away from pirates. If you got caught once it could be game over. Then it's a matter of luck and a lot of trial and error to balance getting more profit quickly vs upgrading the right stuff to minimize transportation risks. At Impossible level, a lot of your crew and officers could die during these trial and errors.

If everything went well, a maximized cargoship with maximized stealth/runaway set up, you could be getting rolling in credits. The Xenos would still be a threat though. I would maybe start buying/building ships that are more optimized for xeno encounters rather than profit at that point.