In terms of gilbuyers and sellers having an impact on how fun your gaming experience is, the fact that people can buy gil with real money means that money is brought into the game unnaturally – money which is being used by someone who wouldn’t have had it otherwise. The more people who take advantage of this, the more likely it is to cause inflation with prices of certain desirables being far more dear than their worth. Yes it can be annoying to have to work that much harder to get that one overly-expensive item that’s missing from your repertoire, but everyone has to put up with that at some point in the game anyway.
Overall, it isn’t something that should influence whether or not you buy the game. If you don’t condone gilbuying/selling, simply abstain from the practise and enjoy the game without forever condemning gilsellers to hell. .-.