OP is already purchasing the Facebook group, he is not interested in buying, he needs help and answers, not agents.
First of all, welcome to BHW
@Mithoty
There is always a risk... Securing a smooth transition should be a top priority.
It can be a problem if you have no trust in a seller.
What I would do, if there is a third person who knows you and him/them, include them [if they are trustworthy].
Or, meet halfway, if he/them doesn't want to give you admin rights if you ask for it before you pay, pay a part so that even if something bad happens, you don't lose all the money.
Of course, losing money shouldn't even be an option, but when doing transactions like this, you simply have to be ready for anything.
Feel free to ask whatever interests you, don't hesitate.
Have a nice day and once again, welcome to BHW.