The process and pitfalls and failed adoptions?

Hi, I’m hoping a few of you seasoned folks who know more about this could share your insights and experience as I’m trying to understand 5 things about the process to avoid the pitfalls and fake agencies. 1. Is it correct that in order to go through with a private domestic adoption that you first have to find a legit agency that does it, you then apply ( pay fees) to get the ball rolling, you then have to go through a home study and adoption training which can take up to 6 months to a year, you are then matched with a mother and child immediately or it can take several years? Have I missed anything out? 2. If the child you are planning to adopt is in another state you may have to stay in that state for a period of time until all the legal paperwork is completed? ( and Is this period after the home study or during?) 3. I’ve heard that some applications get rejected because the social worker is unreasonable, they think you are still grieving the loss of a biological child, or some other issue? 4. Now this is the big one that confused me. I’ve heard that some prospective parents going for a private domestic adoption end up having it fall through but that before it did fall through the prospective parents had the adoptive child home with them for a few weeks up to a few months before the mother decided to take the child back. First, by the time you have the baby/child in your possession is not the paperwork all completed and they have relinquished the child? Or is it because every state has a period of time after you hand over the child where the mother can revoke her decision and take the child back? And if so what is that period of time? 5. Is it true there are fake agencies out there that are scamming people looking to do domestic adoption? And how can you tell which are legit and which aren't? That’s it. Thanks kindly.