I believe whether you go with an agency or chose to navigate on your own finding the right family, it comes down to the people you choose. No agency can guarantee what a person will do in the future. If you are able to communicate with adoptive parents prior to your decision you can get a feel of their honesty. Not everyone will follow through on their words in this life, but there are people who will. To be very honest when I first went into the hopes of adopting I was afraid of an open adoption. I was afraid if I built a bond with the babies mother that I would make it harder for her, I was also afraid if later on the child reunited with their momma they wouldn't want me in their life because I wasn't their real mom. It took me being a foster mom to realize that none of us have control over what the future holds. It made me realize how important an open relationship is for everyone. For the adoptive parents to know the genetics of the child they will raise, for the child to know their story and for the birth mom to be involved in the future journey. My best advise is to ask questions to any couple who may be fortunate enough to be part of your journey, express your concerns, learn about their experiences so you know them at their core. Trust your gut. There are amazing people out there just longing to raise a child, just never be afraid to make a laundry list of questions and put it all on the table. If the answers aren't what fills your heart then they aren't the ones.
Honestly the decision is up to you... I have friends that have went down both routes and both gotten successful results and some bad results.
i have given four kids up for adoption. the first couple was amazing, the second couple was lying and decitful, and the third adopted both the last two children. but by law nobody can make the couple do what they say, becasue your signing over all the rights over to them. i learned that with baby number four, they told me that it was whatever i wanted at least until i signed the papers over, i was mad and hurt for the longest time, and the couple who adopted my last two children made me realize i did what was best, but its there children, its there child, and yuo just have to remember why your doing it, and by the grace of God, I found what i was looking for, and got what i wanted, but just know, by law your signing over your rights, you dont get to make that decision, neither does the agency, and some people just are liars, but if you continue to seek God he will tend to your broken heart. Good luck and God Bless