How do I sell something on the internet? (accounts/scripts ect)

I am not new to creating hacks, but I am wondering what would be the savest way to sell something on the internet?

In forums like this one (not allowed to name others in here) I see tons of people selling accounts, hacks, scripts, ect but they always ask for private contact (eg skype or email).

Of course it wouldn't make any sense to discuss this while everyone can read it, but thats now what I mean.

I would like to know how the money transfer is done, who goes first, how to prevent scam, ect ect.

Can anyone who is familiar with this give me tips on how to do it properly?