The likelihood of settling them first time you let them out is minimal, so you will have to see the man you are getting them from to ensure that when they do return home they are not welcomed by feeding or being allowed back into nest boxes or the like. I break 99% of the birds i receive by letting them out late in the day in dirty weather and hungry. Ordinarily i will feed in the afternoon on the day prior to letting them out, so when they get out the next evening they are really hungry. My own are treated exactly the same as it is them the newcomers learn from. I let my own out first to have their fly then open the trap to allow them to make their own way out amongst mine. Feed them a little seed on the landing board and i encourage my doos to come onto the ground so the new ones will follow, i try to get them to fly up and down from loft to garden as often as possible to get them used to landing on the loft. If you can do this you are most of the way there. Tell the present owner not to feed any birds that return to him and to put them into a basket as soon as possible after their arrival. As soon as you get them back home feed them, if you do this they will settle quickly. Though probably NOT first time they take off into the air! How long you keep them in before this depends on whether you think they are used to you and the new surroundings, usually when they answer my call/whistle with the rest of the birds at feeding time, then i try them out. You could pair them up to some of your pigeons and get them down to nest before they settle properly. I NEVER pair 2 strangers together when they aren't broke to the loft, always pair them to my own birds to help them out. All of this is jmo, but it does work for me so it should for any one who tries it.