I don't think there is a problem with me raising up "brainless twats" anyways. Sure a newbie who has yet to "pick up a clue along the way" might be able to afford one or two easy level ups with my service, but the cost does go up as you are signing on for more than one level. It isn't just 100 gil extra... that would be too easy to get and yes, a waste of my time.

Here's an example (one of my previous jobs in fact)
There's a Rank 5 War35/Nin17 who wants to be a Thf/Nin rather than War/Nin, so he gets me to power-level him to level 15 (since finding parties is sometimes difficult for Thieves especially in noob areas like Valkurm until Sneak Attack is learned) He is a level 5 right now and solo'ing is getting a little bit slow for him, so he pays me to take him to level 15. I earned 600 gil levelling him up to 6. That's not a lot of money, I admit, but it is a very easy job raising someone from 5 to 6. The way my system works is that you're taking the level you're earning and multiplying it by 100gil. So instead for 100 more gil for level 7, I got an addition 700, then an additional 800, another 900, etc...
The full 5-15 job resulted in 600+700+800+900+1000+1100+1200+1300+1400+1500 gil. This is not exactly a service for people who don't know what they are doing, for most of them would not be able to afford it. The reason why someone might pay me this much is because it is an extremely quick and safe couple of level ups, and not too pricey for the experienced players. He got to level 15 in about 3 1/2 hours chaining Even Match and Toughs pretty much nonstop.