1st, vmxa, thanx for replying to my earlier question about getting techs (or not) by conquering other civs.
2nd, i am confused about a rep./trading phenomenon with GPT-involving tech-buys. I am playing Japan in Demigod. Throughout the game, I have been buying tech from the other civs, in part with luxuries, resources, and GPT.
Suddenly, starting around 1270, i'm early industrial they're mid-late industrial, my trading partners don't want to do GPT- or resource-involving tech deals.

But they will sell me tech outright, and I can buy resources using GPT and my own resources.
For example, India will sell me medicine for 2600 outright. They won't sell me medicine for 2400 outright plus a favorable GPT. At 2400 outright, I get "we are getting close". If add 20 GPT, I get "would never accept". If I jack up to 366 GPT (current income) & Incense plus 2400 outright, I get "doubt they will accept". But they are happy to sell me saltpeter at 105 GPT, or 58 GPT plus incense.
I have gone back through the turns over which this kicked in, and I can't figure out what is going on. No trade deals I was involved in were broken in any way. I didn't recently declare war (I razed some cities a long time ago b/c my culture is LOW.). My war/peace/trade relations with 3rd parties don't seem to be relevant. I'm not more powerful than India or the others.
Does this just happen at Demigod or in the Industrial Age? This is my first experience doing tech buys - at Emperor, I could catch up in time to dominate or win the UN vote.
Thanks
