I guess the bigger question is..

How do you know what the person is you are trading with? If I say I'm a Warlord, how would you know I'm not lying? Who's to say that you don't have a bully Warlord in your sector that you want to get rid of? Why wouldn't you ally with someone that was a researcher? I would think allies of any sort go a long way to helping you reach your goals.

As a trader your best economy will come from trading. The more trade routes you establish the better. Think Ferengi in Star Trek. You're more than happy to trade with someone as long as there is something in it for you, and you get what you want. Who cares what other people are doing. I certainly think if you limit yourself in "who" you want to trade with, you could find yourself in a dire situation quickly.

Sure a researcher doesn't offer you anything other than an increased economy, just like the warlord, and while they won't have the muscle of the warlord with stealth ships, and star collapsing abilities I certainly wouldn't want to get on their bad side. If you needed help a researcher isn't a bad one to have on your side if you both want to work together to rid the universe of others.