[anarres]

Step 1: Go to war with a technologically advanced civ. Note that you have to be prepared to fight them for a long time and you will need to have a decent income (not gpt, just the ability to turn down science and lux to 0% and have a good gpt mid-turn), so Democracy is no good, as is having a small military. I tend to do this in Republic (extra commerce) and I get them to declare war by making them furious with demands and then demanding they leave or 'steal tech'.

Step 2: Wait 6 turns until you can talk to them.

Step 3: Make peace, but in the deal get all the techs you can for a huge amount of gpt. You can turn all the sliders down and set all your citizens to work the high-commerce tiles (like water tiles) to do this.

Step 4: Declare war, set your sliders/citizens back.

Step 5: Rinse and repeat ad nauseum.

Now the only thing that makes this worthwhile is what I consider to be an oversight: The ability to give GPT for techs when part of a peace treaty, regardless of your rep.

If you have a good rep you will ruin it like this, and going to war is not needed to screw them the first time, ever. I tend to leave this until my rep is shot or I am desperate to catch up in tech and have no other means to do so.

Note that this is especially powerful on Continental maps and Islands. Nothing like a war when the AI can't reach you.