In Thailand, there are some expats who are always trying to circumvent the system to get a visa or extension by dubious means. I'm sure the same is true in Vietnam.
It usually comes back to bite them sooner or later.
Best to stick with means that can openly be described on a forum. If you have to PM somebody to get details, it's probably not a good idea.
My advice would be to find a reputable and well-informed professional agent who can advise you with sound options that you won't lose sleep over.
Just my opinion; take it for what it's worth.