You never know when rehoming or selling an animal if the person who buys it is going to be good. The best you can do is question them thoroughly and get their name, address, phone number, who their vet is and if they hesitate at all to give you the information, then rule them out. It's a gamble and you have to go with your gut feelings about people.
I can sell babies much easier than I can rehome the adults we get in. One thing with the babies is I always have a waiting list and waiting that 3-4 months to get a baby turns those in a rush spur of the moment off. With the adults there is no waiting period as they are here right now. I've had people ask about a baby and when I tell them the wait time then they want an adult. Obviously they are in a rush and it's not going to happen.
While I do not agree with getting rid of one to make room for another, rescues have to do that. We only have so much room, time and money to go around and when you reach the limit you have to re-home them. Be careful re-homing girls. There are a lot of people looking for cheap hedgehogs to breed. Buying breeding quality babies is too expensive so they go to craig's list, kijiji and the rescues trying to get cheap or free. That's why I have so many adult girls staying here.