This game is on demi, set to large continental, warm, wet, raging, only 5 AI. I actually wanted 7 rivals, but somehow I messed it up. I didn't check F10 in time and when I noticed this, I just carried on playing - so I stumbled across this deal.
The deal *could* have been even better, but monarchy on top of it would have been too much. I rather took constuction, mm, all their gold and spare gpt and the (not displayed) worker instead of construction (or mm), monarchy and less gpt.
Monarchy is dead end and I had 3 native luxs, that's why I didn't want to use it at that time anyways.
My other contact was Rome (India knew them), neither knew republic. India might have known the other civs, but I guess republic was a world-wide monopoly tech. Though I researched WC and alphabet on my own and then even
traded for writing, I surprisingly won the philo gambit (CoL) which most probably featured that monopoly in the end.
A bit later, with additional contacts, republic had not been sold around by India and I could trade it for monarchy (spread) to Rome.
Amazingly, India's (indeed gov=monarchy) total spare gpt was even higher than 55gpt, because they already paid me 5gpt for a peace treaty [at some point, Ghandi sneak attacked... as usual

].
The treaty was put up 2 (IIRC) turns earlier (rep was not due yet) and I noticed their huge spare gpt during those negotiations by testing it. Surely I praid to get to rep first
and that India wouldn't give the gpt to someone else meanwhile.
I also have the feeling that some civs, such as India, England and France, often have a lot of gpt to offer. It seems that the commercial traits fits to their 'build'-flags.