True, if you assume the accepting party has the best intentions of the child at heart. Come on, as a philosopher (as opposed to the rest of the posters on VN) I would expect you to make no assumptions when articulating your argument.
The accepting party could be into the human trafficking business. Sex slave business. Maybe the accepting party is a dirty old man who would kill to be able to buy "pure" children to satisfy their own perverse vices (similar to Sandusky or Brian David Mitchell who kidnapped Elizabeth Smart; btw he had a wife who could easily have played the part of a sympathetic grandmotherly figure to secure a child if need be. don't underestimate a child predator's ability to fly under the radar. hell look at Sandusky, he has adopted children). Presuming that the accepting party are good parents with admirable morals is quite naive. It is akin to believing that humans are inherently good or altruistic. They are not.
Finally, you seem to be operating under the notion that two consenting adults can engage in any economic transaction they please. As a libertarian, I completely agree. If a girl wants to sell her body or her virginity then I believe they have every right to do so. The problem with this argument arises when the "economic good" is a third party who does not have the ability to consent. Which is the case when biological parents are in essence selling their baby. As I said before, when dealing with a baby/small child, it is not a bad idea to have a third party make sure all things are done above board. The minor ought to have someone independently looking out for their best interest.
The money which is collected during an adoption does not go to the biological parents, thus eliminating any intentional economic incentive on their part. The money is primary used to address both the legal and health needs of the child. Again, I think this process should be more efficient thus increasing the economic incentive for adoption by willing, good parents. And yes I understand the waste/bribery foreign governments collect in the name of adoption. Yet another reason American adoptive parents should focus on adopting children from the homeland instead of abroad.