Sometimes you don't have the choice. I stupidly got into an argument with the head of my immigration office and now she won't even do a 90-day for me. Thank goodness I can do it online.
Who is holding your hand in depositing money in a bank account? You just need a Thai bank account with any amount. You have to provide a lot of documents and physically go to the office at LEAST once and usually more than once. Plus you need to go to your bank and pay fees for statements. I rather just mail in the 3 things I mentioned and wait for it to come back with my extension. To me, not having to do any of that other stuff is worth paying someone to do it for me.
Not sure if I could be called any of those but I've applied and got an account to do my own reporting online. Not that hard to get. I guess this doesn't answer your question as to what is a possessor, sorry.