How to buy an rs3 Account on sythe safe?

Hey i want to buy an rs3 account on this.
Iam new to this Forum and i have some questions. Is there some rules to follow when buying something? I know other forums where u have to send other users a trade request. When i dont do this i cant report the user when he scammed me.
And are there some tips when buying an account? What Account information should i get from the other user to be safe that he cant recover the Account? Also should i make a video from the trade so i can report him?
(Sorry for my bad english, iam german)