Trev said:
( the only case I know where they will accept such a deal where your reputation is ruined is a peace deal where you pay gpt to them, I do this by including techs from them as part of the deal), if this deal is not broken, then that civ will do regular gpt deals with you again until another reputation lapse.
You have just described a major (in my opinion) bug. Generally, if you break a gpt deal (where YOU pay), the AI will not accept gpt from YOU anymore, unless you do it in a peace treaty. So all you have to do is play a huge map, declare war on half the civs, and continuously give them gpt for peace and demand techs in return, then declare war the same turn, and the minute they beg you for peace, do it again. Only the peace treaty makes this kind of "dealing" with a broken reputation possible, that's why I consider it an exploit.
In one game where I started in a desert and had only 3 good cities, the rest size 2 or 3, I've been able to catch up from middle ages to late industrial in a matter of 10 turns, without paying a single penny, but by declaring war on all civs on another continent (there were about 10 I think), and then sitting back and waiting for the "war" to end, just to be able to give them maximum gpt that I could and declare war again. This makes the game way too easy, so I recommend to not use this exploit.
Oh, and by the way, when I moved from vanilla to conquests, I too noticed that very seldom do AIs have gpt available, even if they are the most advanced nations and ahve thousands of gold in treasury. In vanilla they definitely used to pay more gpt more often. But that just makes the game more fun because now you can't just buy one tech and sell it to everyone for huge gpt amounts, at least not on standard size maps where the 100-300 gold most AIs have is not enough to compensate for 2000+ you pay for a tech.