Can I actually interact with trade ships in space?

Solution 1:

Whilst I have not done this myself, I have read several times on the official forums that other players have. If you have the items the ships are seeking, they are magically taken from you and you are automatically paid for them.

I can only assume that you get paid a considerable amount more than you would get selling them at any station or you could end up quite upset if you lost out on potential profit.

This wouldn't stop situations where you had bought the cargo for a "Please bring me X tons of Y" type mission from a bulletin board and the cargo was taken from you.

Edit: Confirmation of the "fly close" mechanic. https://forums.frontier.co.uk/showthread.php?t=96996&p=1507483&viewfull=1#post1507483 This thread also clarifies what is a "luxury item", in this case players are trading Progenitor Cells with these mobile markets.

Solution 2:

I just sold 212 cargo of battle weapons to the Seeking Weapons dealers. They paid 1,599,000 for all of them. I paid about 6400 each for them, and their deal comes out to 7500 or so. Made over 300K profit on one quick run. The bonus is that you dont have to sneak into a station and possibly get fined. You fly close to them 1.5km or so and they auto take it out of your hold. Instant payment in the info window.

Edit, personal weapons dont count. I tried 10 units of this and nothing. Wasted my time on it. Dumped those and bought the above Battle Weapons and made bank.