A. What can be acquired through the Kinyan?
All items, whether moveable objects [i.e. Mitaltilin] or land [i.e. Karka] may be acquired through a Kinyan Suddar [otherwise known as Kinyan Chalifin]. This applies whether to a sale or to the giving of a present.
B. How it is done?
The buyer of the item, or receiver of the present, gives the seller, or present giver, a vessel of any value and tells him that “You are acquiring this item in exchange for the land or item that is being sold or given to me.” Practically, however, the custom today is to no longer have the buyer/receiver tell the seller/giver the above statement, as it can be assumed that it is being given to him under these premises. [In the event that witnesses are present then the Kinyan is done by the witnesses, as explained in Halacha D see there!]
C. Conditions to validate the Chalifin:
The moment that the seller acquires the Sudar through taking/lifting [Meshicha] it, the land or sale item is acquired to the buyer/receiver in any area of the world that it exists. The transaction is valid even if the buyer/receiver did not make an acquisition on the item being bought/received and even if money was not transferred from the buyer to the seller, and even if a document was not written between the buyer and seller. No side of the parties may retract from the transaction once the Chalifin was done.
It is not necessary to have witnesses who witness the transaction, and so long as both the buyer/receiver and seller/giver admit to the transaction it is legally binding irrelevant of witnesses. Likewise, even if the transaction took place in front of Pesulei Eidus, it is valid being that they admit to each other that the transaction took place. It is however advisable to have witnesses view the transaction in order so neither side can deny it having occurred. In the event that witnesses are present, then one of the witnesses is to give an item that he owns to the seller/giver and have him acquire it as the Sudar/Chalifin transaction. [This is in place of having the buyer/receiver give the seller his item.]
- Is Kinyan Sudar a valid acquisition when done with a gentile buyer/seller?
All items, whether moveable objects [Mitaltilin] or lands [Karka] may be acquired through a Kinyan Suddar. This applies whether to a sale or to the giving of a present. The buyer/receiver gives the seller/giver a vessel of any value. The moment that the seller acquires the Sudar through taking/lifting [Meshicha] it, the land or sale item is acquired to the buyer/receiver in any area of the world that it exists. It is not necessary to have witnesses who witness the transaction, it is however advisable to have witnesses view the transaction in order so neither side can deny it having occurred. In the event that witnesses are present than one of the witnesses is to give an item that he owns to the seller/giver and have him acquire it as the Sudar/Chalifin transaction.
 Michaber C.M. 195:1; See Toras Hakinyanim chapter 4 for a through summary on the topic of Kinyan Sudar
 Michaber C.M. 195:1; 203:1
 Michaber C.M. 195:1
 Rama C.M. 195:1
 Michaber C.M. 195:1
 Michaber C.M. 195:1; 189:1; Smeh 123:21; Rambam Mechira 5:9; Tosafus in Baba Basra 40a and Kiddushin 65 and Sanhedrin 6; Rashba in Bava Basra 40a in name of Rabbeinu Tam and Rif; Ittur, brought in Maggid Mishneh on Rambam ibid
The reason: As the only reason that witnesses are used for Kinyan Sudar is so neither party can contradict the transaction, and lie and deny it having taken place. [Smeh 195:4; 123:21]
Other opinions: Some Poskim rule one is required to have witnesses by the Kinyan Sudar/Chalifin in order for it to be valid. [Rashbam Baba Basra 40a; Shita Mekubetzes ibid in name of Raavad; Raavad Mechira 5:9; Tosafus Baba Basra 144a; Meiri Baba Basra 40a in name of Geonim] Some of these Poskim rule it suffices to be done in front of one witness. [Rashba ibid in name of Raavad] This dispute only applies when doing a Kinyan Chalifin/Sudar in order to finalize the sale. If however one is switching items with another, then it is valid according to all even without witnesses. [Toras Hakinyanim 4:12]
 Rama 195:1; Rosh 66:8; See Chidushei Harim 195; Smeh 2418; Toras Hakinyanim ibid
 See Smeh ibid
 Rama 195:3; Tur in name of Rosh
The reason: As today most Kinyanim take place not in front of the receiver/buyer and hence the custom became for the witnesses to give the seller/giver the item of Chalifin even when the buyer/receiver is present.[Rama ibid]
How it works: The witnesses act as the Shliach of the buyer/receiver and they thus acquire the item on his behalf through giving him their item. [Initial explanation in Ketzos Hachoshen 195:9; See Ramban 101; Toras Hakinyanim 4:18 footnote32] Alternatively, the reason it helps is because one is able to give an item to one person and have him acquire it to a third person. [Final explanation in Ketzos Hachoshen 195:9; Maharit C.M. 21]
 Rabbeinu Tam brought in Shach ibid; See Shaar Hakolel 32 in name of Maharil that Admur was accustomed to do a Kinyan Sudra with the gentile by Mechiras Chametz in order to benefit this Kinyan as well according to Rabbeinu Tam.
 Shach 123:30