Legit high class KTV will NOT let you have sex in the KTV room. If there is an offer of sex and it is suggested to you that you do it in the room, RUN, don't walk, OUT OF THERE! It is more than likely a scam. Every KTV scam I have heard about involved having sex with the girl in the KTV room. KTV is NOT massage or sauna and is quite often a legitimate business. Furthermore, there are many KTVs where the girls do not go with the customer or it's up to the girl whether she wants to go with you. If a girl offers herself in the room, there's usually an ulterior motive, one that could be potentially harmful to you.
Let me recommend that you stick to KTVs in 4-5 star hotels. Although these places will be a bit more expensive, they will not scam you. They have too much to lose to risk their reputations. When you enter the KTV, make your intentions clear to the mamasan that you want to take the girl back with you. Many places have two groups of girls, one group that's available for take out, and another group that is not. The piece moody wrote in the other forum is as good as any on what to expect and how to behave at KTV. Read it twice.