The ones online who (at least claim that they) will cast a spell for you, for a fee? There are far too many frauds and scammers out there.
The thing is, you firstly have no real way to verify if they have done what you need and how you need it. And that right there is a big problem. Secondly, you are only indirectly involved with the process, and but a vague concept to them. Even for the real practitioners out there who offer their services, this does make things a bit more difficult.
The best way to have magical success is to use your own effort to make it happen. That way you know what was done, how, when, and precisely how it was directed.