I always thought getting the abandoned ship locations off the internet and then selling them was a bit...unethical...within the universe of X3.
My experience is only with Terran Conflict, but I think the concepts should be universal.
The basic gist of the whole thing, as a trader, is that you want to buy low (price) and sell at a high price. This can be done based on how much supply the stations have.
So go to each station, and check the supply of the goods they're producing. If they have a lot of goods, the price for the goods will be low. Then buy everything you can afford, and then find some station that will buy those goods. Check if they have a low supply, because then they'll pay more for it.
Eventually, you can buy trading software that will check the prices in the entire sector for you. But they start getting expensive, so when you start you're going to have to do these manually.
There's a logic to what station will produce and what goods they'll need. A good track to start might be buying ore from mining stations. Buy it as cheap as it goes. Ore is a great commodity because a lot of stations need it. Your in-game encyclopedia should have the lists of buy/sell goods, but if not you could check online.
It took a while before I figured out that you can check the amount of supply the station has. After that I started making the big spacebucks.
Edit: You can of course trade a lot of stuff. I guess I just started with ore, and kept doing ore runs until I had enough to buy the software + automated trader.
On this website it shows ore to range from 50 to 206 bucks. So you buy at 50 and sell at 206. Again, apologies if this is massively different from TC in Reunion.
http://eng.x3tc.ru/x3_tc_factories/factory.php?c=NTU3ODg2NTE Here is a guide to Reunion:
http://forum.egosoft.com/viewtopic.php?t=98222 It mentions Ore as something like 100%+ profit.