Questions on trade

Anytime the box is green, the trade will go through. The object is to put as much on their side and as little on your side as possible while keeping it green. After you've set up what you think is a good trade, try to see if you can get money from them, especially over a period of several months (can get more that way). Experiment and see how much you can get. Then see if you can add influence.

Generally, they value military techs more, so research those and sell it to them.

Don't ever give them Diplomacy techs, 'cause those will make your future deals worse off, as how much you can get is dependent on how much better your diplomacy is compared to theirs.
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On the other hand, they'll also tend to build their military techs first, so it's often hard to come up with a military tech they don't already have.

If you can beat somebody to Deflectors in the early game you'll be able to get just about anything you want for it, though. Aliens place inordinate value on Deflectors (defenders), Interstellar Tactics (frigates) and any ship tech of Battleship or above.

I made myself a little spreadsheet of what bonuses, achievements, ships, etc. each tech gives and how much it costs. Generally with decent diplomacy skills, you can trade at least 1:1 (offer a 200-cost tech, get a 200-cost tech in return). Getting 3:2 or 2:1 is not unlikely, and even 3:1 is doable with enough diplo advantage. If you can trade deflectors or Interstellar Tactics away to somebody, you can probably get all their other techs and trade goods and a hefty, long-term payoff too.

Sell deflectors if you an and buy defensive phasers if you want to use hammers.
Buy diplomatic translators at any cost if someone else built it. Never sell it to anyone, unless you plan to kill them on next turn.
You can buy any trade good but shouldn't sell grav accelerators or influence ones (galactic guide book) to a major.
Other than that, a 'good' trade depends a lot on your diplomatic skills and the level you play. Incredible ai's giving you 10bc for deflectors means you have a huge diplomatic advantge, for instance, but you won't want to do it. They will be likely to give you 33 techs instead of 10 bc, so rather take that.
Some of the best trades imo are when you give money now for something or get money over 100 turns from the ai (you have to type 100 by hand, the slider stops at 50).

I've got a question on trade goods while we're at it. If you develop a trade good and sell it to someone, can they resell that trade good? Or do you exclusively own the right to sell it to anyone? If they can't resell it, then I think I may have missed quite a few good trades.

Good question...

But if they can't resell it, isn't that a good thing because you have the monopoly on selling it?

AND when you buy a trade good, do you get the advantage it confers

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They can't resell it. You have the monopoly. They just get the benefits.

Yeah, it is a good thing. The bad thing was that I didn't know that so I didn't sell it to them at all when I should've. More money and tech!

I find they don't really pay that much for trade goods, esp early on. However, they will give nearly ALL their inf points for even the earliest goods. save them for when you have a UP vote comming up the next turn. Just one strategy of many the trade goods are usefull for.

TG used to be valued a lot. I mean really much. So now their value has been adjusted quite a bit.
I always sell all my TG except Diplomatic Translators to new minors in exchange for all their cash over as long as possible when they appear. This prevents other races from taking their money, and I can't sell them tech since they have all the same as me. The result is usually good enough in terms of money, though the main idea is to cripple the minor so they don't start becoming powerful and I can invade them safely.

LDiCesare...can you do this on maso too ?

Yes you can do this on maso with all minors except the starting ones.

I find on maso you can still exploit the Alexians for money, just not the Carinoids for some reason.

Alexians could be exploited, but no longer can (at least not more than a few bc in myu experience).
This has been done in a patch sometime before 1.10. Jordanvmp, which version do you use?

One technique I use to maximize trade is to always start by including all my cash, then trade for the most techs, then lower the cash to the minimum required to make the trade. I have found out that often enouth 12BC was all I needed to get the extra tech!

Errr, I'm on version 1.11, and I can still exploit the Alexians on Maso.