Here is an interesting article, written by a chess grandmaster, on how to trade information with alien civilizations, assuming they are ever contacted. The article proposes that at interstellar distances, the only realistic form of trade would be a trade in information -- such as technology and scientific knowledge. He suggests that the best way to effect such trade would be for civilizations to send one another the code for artificial intelligences that would act as their "brokers" of sorts. But there is a problem with his proposal. While it certainly is based on less anthropomorphism than the current SETI and NASA idea of sending binary encoded pictures back and forth, it still makes a number of unwarranted assumptions about our potential alien correspondents. In particular, I question the assumption that there would be any need for trade or negotiations at all! For example, given that we establish contact with an alien civilization that is, say, 300 light years away, and given that there is no form of faster-than-light travel available, then it would take at least 300 years (but most likely much, much longer) for either civilization to send a physical spaceship to the other. At time-scales of that length it would probably not make sense to visit one another at all. Given that, why withold anything from one another? Instead, it would make more sense for both civilizations to just send each other everything they know to date, as a gift of sorts.
It would still take 300 years for this data-gift to arrive, but that at least would save both civilizations a lot of time in their respective futures (assuming they did not already know everything in the content of the respective messages). It seems to me that if there is little possibility of ever physically interacting, advanced civilizations would be likely to adopt a policy of altruistically sharing all their knowledge rather than withholding it from one another. Why? Because there is little to no risk of doing so, but at least there is a near-guarantee of benefiting the recipients. In a situation where taking an action is unlikely to cause harm but guaranteed to bring about at least some benefit, advanced civilizations would very likely take the action (assuming the cost to them is not on a scale where it is harmful to them).
Why would they take such action? First of all by demonstrating good-faith to that degree the senders of such a "gift of knowledge" would have at least some chance of receiving a reciprocal gift from the recipients, which would result in eventual reciprocal benefit to them. But even if no benefit was ever expected or recieved, by the senders, they would at least be benefiting the recipients, which, to a truly advanced civilization (i.e. one that is advanced on social dimension as well as technological dimensions) might be satisfying enough in-itself.
This also makes sense from a sociobiological perspective. According to sociobiology altruism is ultimately selfish and based on the drive to spread one's genes to future generations. But this argument doesn't explain cross-species altruism -- for example, where a person or an animal takes care of an orphaned baby animal of a different species. In such cases of altruism there is no direct or indirect genetic benefit to the initiator. So why does it take place? Perhaps it is due to a desire to spread Life itself, an even deeper motive than just spreading the genes of one's own family or one's species. Perhaps truly advanced civilizations identify with all Life to some degree, and are motivated to help it evolve and prosper in the universe. They might also have a spiritual/religious perspective on generosity -- for example, they might believe that helping others is both "the meaning of life" and the most satisfying reward of living. Even the religions that have arisen within our own quite primitive and violent civilization all suggest that kindness is the highest ideal, and perhaps alien civilizations have also come to similar conclusions.