It's not easy.
Let's say that you're becoming successful with that group and you're building up a community. The likely of being bombarded by scammers on your group is possible.
But you can maintain them through you alone or someone that will work to filter your members. If there's none that you can see, I have the same thing to say about in the gambling discussion, there are too many pickers and predictors there that you can find.
As the group is growing, expect that there will be trolls or scammers that will try to explore the channel. It is true, better look for prediction threads in this forum in the gambling discussion boards. There are so many good insights already that you can get from the members here. For me, that's more than enough. But maybe, the OP has other goals for his group later on.
Yeah, that's the part that he has to endure and filter as much as he can.
A growing group really is a vital process for someone who's able to manage it successfully. There will be imitators that are actual scammers playing their scheme on that group.
That's why it's not going to work that easy or else, he has to go through several ups and downs before he's able to manage it wholly. Unless he has already a plan for its management.