I still haven't seen a credible basis for banning lump sum gold deals.
Neither have I, aside from self-pillage deliberately. I have asked for a credible basis over and over and over and over again. People have largely chosen to either ignore this or answer by saying that a credible basis is not required

. Somehow, rules were made without that credible basis which is very frustrating.
I doubt that this alleged exploit has been researched enough to validate its detrimental effect on game balance.
I'm virtually certain it has not, given both the behavior of Firaxis and the complete lack of evidence by HoF that the research exists. However, it's a high and somewhat unfair standard to set on HoF to overcome the incompetency of firaxis...I understand the HoF desire to protect the integrity of the rankings but at the same time...these rules still need basis if they're to claim that they do that.
Where's the proof of its exploitative value that is out of balance with the opportunity costs and risks in using it?
Where indeed? Does anyone have this proof? If so, why are we hiding it for weeks/months on end when the rules so badly need the support of such proof? Players and observers have no choice but to conclude this proof doesn't actually exist given no evidence of it.
The exploit of trade agreements for lump sums of gold is the only thing we are banning. I would think that the benefits of systematically pulling in hundreds, if not thousands, of gold as fast as the AIs can replenish it is pretty obvious. You need gold to engage in RAs and RAs blocking. You need gold to buy buildings and units. You need it to upgrade units. Gold is the resource you can use to get other resources.
You say this repeatedly, but never put forth evidence of an actual exploit. Many tactics, including some that have been listed as banned, have costs that make "systematically" getting lots of gold impractical. Declaring war to take a city you just sold is an excellent example; the cost for doing this is real and on the "ban this" side of the argument, ignored.
It's easy to pass off tactics you don't like as an exploit. The reality is that not all lump sum for per turn obligations are created equally, and neither are all means of breaking those obligations.
The only thing about war we are banning is when it is used as part of a systematic strategy to break deals without actually fighting. The bit about selling cities and taking them back is in response to a specific question. I don't know if it is practical but my understand was that it involved to selling off a few minor cities and immediately takimg them back before the AI fortifies them. Let them recover a little and repeat. That is it.
Yes, "that is it", but where is the exploit in doing that? When you do this repeatedly, you sacrifice RA with the target civ and possibly others. You become a "warmongering menace to the world" because you're capturing cities. You have opportunity cost investment on units required to take the sold cities.
In making paragraphs like the above, you fail to acknowledge any of that. Those costs make for some *expensive* lump sums of gold if you use them in the wrong situations. This is a tactic that, if employed improperly, can lose games. It has nothing in common with pillaging your own resource to break a deal; there is significant strategy and game knowledge required to recognize that said activity is better than alternative options...this tactic is *consistently* weaker than many, many tactics you allow! This is why enforcing against it is arbitrary and, to the HoF, dangerous precedent.
I am not interested in fixing Civ5 many ills (I don't have the tools or the time.) or trying to eliminate randomness from a game built on randomness. Please quite trying to push other agendas or justify hanging on to the crutch of a lot of free, easy gold.
I don't think anybody short of a major professional organization greater than firaxis can fix the many ills of civ V.
However, HoF is a competition. Let's be reminded of something crucial:
The essense and spirit of the HOF is that everyone is playing under the same conditions and following the same rules. The HOF is intend to allow players to submit their best games for comparison with other HOF players on a level playing field.
This implies a higher standard than "the point of HoF is that everyone agrees to abide by them". In arguing against random-ness and the need to spam games looking for lucky outcomes, players are seeking the alleged point of the HoF rules: a level playing field! Not everybody has the time or energy to farm random chance until it's favorable, and doing that has never been confused with "strategy" (something civ advertises it is). There is no "other agenda". The agenda on this thread by most people posting in it is fair, reasonable, and consistently applied rules that have some basis/justification toward better competition. In making arbitrary bans, the HoF takes away from the skill and strategy of gameplay. In leaving room for doubt in whether a certain tactic is banned (especially rejecting something not explicitly stated yet), the rules cheapen the competition.
The crutch isn't "free, easy gold" (which you've chosen to ignore that in many cases isn't free at all in making this post), the "crutch" is sensible, competitive play based on the game in which players are competing...and at this point simply figuring out based on the rules what can even be done!
The emphasised part is not stated in the rules in the OP. Currently the rules imply all LSG deals must complete their term (unless the AI breaks it).
Indeed. I dare say this might cause some confusion of the actual HoF rules. One seems to be a distorted version of the other...
The rules need some major help, and I think as a community we've no choice but to work together on it if we want fair and reasonable rules. We need an agreed-upon basis for the definition of "exploit", and then banning something requires the activity to meet that criteria. We need to flesh out the settings that actually create the most level playing field possible in civ V hall of fame. What we do not need is random bans or rules thrown around without basis, or for ANY one person's opinions to dominate/be final without justification.
What's the best approach for doing this? Probably one thread at at time; each with a specific focus on a given part of the rule-set.