QUESTIONS RELATED TO IN GAME ACTIVITY: 1) a. Yes b. Sold gp/accounts c. no, it is against the rules d. no 2) Existing business 3) I could imagine so yes, seeing how successful and how common bots are within the game.
QUESTIONS RELATED TO OTHER WAYS OF MAKING A PROFIT OFF THE GAME: 1) Me? I could if I wanted to, but I don't have the motivation or starting cash to pull it off. 2) PKing seems to be the most watched streams for RS players, I also see some PvM streams be successful while most other styles usually fail to draw in any sort of audience. 3) PKing. 4) Maybe for people who were popular before streaming and a one time thing, but no generally.
QUESTIONS RELATED TO THE IN-GAME ECONOMY 1) Any period of time in which bots were busted on a major scale. Aftermath of EoC being launched with many repercussions throughout the years because of it's effects. And when a higher tier of weaponry/armor is released. 2) On release, prices of new items with a certain "op factor" are generally known to be unreliable and fluctuates on a grand scale. However, with the help of price fixing by Jagex, this issue has been somewhat solved (although the players still usually change this through overfarming). I believe that all items have had their value changed dramatically throughout the years. Some items which were useless long ago are now sought after by the wealthiest players (party hats). Some items which were extremely useful long ago, is now just a lowly item that is just a broken mirror of what it used to be (Armadyl Godsword). 3) Since I personally do have the funds, I usually enter the rares market to flip. However I have to be very careful as prices are never safe, even for these high ticket items (a lot of times I end up losing more than what I put in). I would not use any third-party websites/software for this as I am very capable of finding information on my own part.
Also, before I get downvoted the "selling of RSGP" is meant more toward "bartering", in terms that I used to give my friends 250k to get their homework answers/Yu-gi-Oh cards. And accounts were more or less the exact same thing.