I mean your service could be flooded with bad predictions. Do you have any criteria you need to met to be qualifies to be a tipster, or to keep your status?
That sounds good, however have you considered asking forum tipsters to join your service?
There are many skilled tipsters on the forum, and if you can convince or sponsor them to put some premium picks on your site and promote your site through their bitcointalk tipster threads, I think that you will be able to attract business.
Heh there are also many unskilled tipsters on the forum who might fear their actual win/loss records being a matter of public record