I grew up in the system and helped raise other peoples kids most of my life, both fosters and relatives. As far as I'm concerned I did my time and then some. For anyone who wants to adopt, especially older kids to teenagers foster first. When things work out you can always adopt the child you foster. But once those papers are signed there's no going back.
My sister recently adopted a family of 3 siblings (currently 10,12 & 16) it was suppose to be four, that she's had for over 3yrs. She was having issues with one of the teenagers and she went to another foster before hand. But the other teenager didn't really speak up during the process, just went with the flow. For what ever reason changed her mind afterwards and REALLY started showing her *ss. To a point where she's been living with me for the past couple of months because she can't go back to their house.
It's a situation that could happen regardless (foster/adopted/blood) but in most cases adoptions work out better when you foster first.