I useally do it if I am surrounding hte minor race. Usually I won't sell them military tech, or if I do I'll only sellit about two generations behind where I am now, so that I still have the edge.

Also, I'll always sell them everything I have for as much money as I can get one turn before invading them, it's too late for them to do anyhting about it, but I get the money they have that you wouldn't normally get by taking them over.

I see no troubles selling any race any tech, as long as you can deal with them having it. I would even sell to empires I am at war...

Depending on the tech and the situation on screen...but they doesn't offer anything worth it if you are at war with them, hehe.

I only sell the tech I doesn't mind seeing everyone getting, I assume the computer will share between themselves or whatever, so before the computer does, if I sell anything to 1 race, I sell it to all races, something for me is better than any trade they might do between themselves.

Never sell a tech you doesn't feel happy to see in the hand of any race in the game, you never know how they may end with it.

I often sell or trade my best techs, it depend on the situation. If my attack is on the next turn, it is irrelevant that they possess my best military technology, by the time they will adapt they will be long dead or negociating a peace treaty after I get what I want (finishing enemies is not always for the best, leaving them 1 planet and selling them your tech and possibly restoring freighter while they consider you overwhelmingly strong is usually far better than 1 more planet in your empire)...especially if they offer something for peace.

And remember, money they give you benefit you, but it is also crippling them. Money they give you is money they can't put elsewhere...and for minor races it is actually extremely harmful to their developpment. Yes they can now build the best ships, but they can't afford it necessarily, especially with all those BC they give you.

Selling tech in any civ-type game is always risky, here's some pointers that Civilization and other 4X game vets probably already know:

Minor races will sell to anyone. If you sell to one and not the rest, you're just giving it away.

Never give or sell techs when it's not your turn. If someone says "Can we trade for this?", you can bet your boots that they will sell the new tech to every other race on the board. This isn't always the case, but if you assume it is you'll never get suckered.

The best way to sell/trade tech, is when it's your turn, decide what to sell/trade, then sell it to EVERYONE at once, even if it means you sell it for a lower price to each individual - the aggregate will make up the difference. Also remember that when they get free techs, just like you, it cuts down their prerequisites for learning even newer techs. So if it's a higher difficulty level, be cautious or you may find yourself the neobarb 'tard of the galaxy looking at everyone's shinnies.

Although i have traded many technologies with the minors, after several turns the majors still didn't have most of them. I'll take this as an indication that they won't just give away techs to each other, which is very good for me. But it just may be because i'm playing on a lower difficulty (sub-normal). What's the case on higher levels?