A Runescape trainer could mean more than one thing. In one way, it means when you hire someone to train your account. A different way refers to a computer program that trains you account for you. Both of these ways are illegal to the Jagex TOS. When you let someone else get on your account that goes under rule 6, Account sharing and trading. (Each account should only be used by ONE person. Account sharing is NOT allowed. You may not sell, transfer or lend your account to anyone else, or permit anyone else to use your account, and you may not accept an account that anybody else offers you)

Using a Runescape trainer program or bot, breaks rule 7, Using third party software.
(You must not use other software to gain an unfair advantage in our games. This includes automation tools, macros, bots, or auto-typers. You may not circumvent any of our mechanisms designed to log out inactive users automatically. You also must not use any game-specific third party software that encourages breaking of our rules, or bypasses the normal navigation of our website, or automatically requests pages from our website, or which endangers user accounts.)

As you can see, both of these are serious offenses and I will explain why. If you were to let someone else train your account, then they might end up changing your password and keeping your money. Then you are at a total loss. This is why Jagex has rule 6. Although many people still break this rule, it's there to help you. Rule number seven is there to keep the game fair. If I was to cheat and get level 80 attack while not even playing, while you sat there day after day working to get there, wouldn't it make your mad?

Jagex wants the game to stay fair. If everyone cheated in it, then it wouldn't be a fun game at all. If you were to pay someone to train your account, usually you would loose a lot of money.
People charge up to 2 pennies per like 10 experience points. Therefore, when you get up to those 100,000 exp areas, you're going to have to pay a lot of cash to this guy. Trust me, it is not worth it.

Any form of cheating in my opinion is not worth the effort. Because in the same time you could have done it yourself and not had to worry about being caught. No fret, no worry, and you will have done it all by yourself. Trust me, its a great feeling to hit that level 60 attack knowing that you did this yourself with no help at all. When you buy, trade, get an account trained or so on, and it gets that special level without you, sure you might be exited to have it, but its nothing compared to the feeling you get when you got that level by yourself.

Runescape trainers could be an exiting thing to try for anyone, but as I have stressed many times, what if you decide to try it out one time, then you come back in an hour, and you're banned? Was it worth it? No, you just lost your account. Remember, curiosity killed the cat. Yes, I'm bringing that old saying out. No matter how tired, bored, or weak you get, never give up. The outcome will be a lot better if you just keep going than if you quit.

If you come across someone that is cheating, report them. If you don't, and your seen by them, you might be thought as a helper to the crime, and thus get in trouble as well. Jagex will look
kindly on someone who reports those who are in the wrong, and sometimes reward them by making them player moderators.

Remember, curiosity killed the cat. Ha-ha, Happy and safe playing!