Paying ads

If advertisers want to get your free ads rank higher in order to ensure that they are above the free listing in a directory, then I'm going to charge. I'll be fine with Google, even if I am using nofollow. Since I have no place on paid search said they are actually paid, I wonder if this is allowed in the first place. How keywords are already in the ads and just because I'm paid, end up getting a better ranking. So all I do is provide them with the best ranking. What do you think about paying these ads?