Responsa for Bava Metzia 216:6

Q. A sold his ground, which bordered on B's property, to C for a sum of money plus C's share in a piece of ground C held in partnership with D in another part of town. After the sale was completed and the title conveyed, B pressed his rights as an abutter. Since Maimonides rules that the law of preemption does not apply to the case where a person exchanges his immovables for the immovables of another, C was advised to persuade A to refuse to accept from B, in payment of A's ground, anything but the particular piece of ground A was to receive from C. Accordingly A claimed that C's piece of ground was very precious to him and that he valued it like the "estate of Bar Marion" (B.B. 12b). B, therefore, bought from D his share of the particular ground he held in partnership with C, and offered it to A in lieu of C's share of the same ground. C, however, objected to D's sale claiming that upon the voiding of his transaction with A he would return to his former status as D's partner, and, having the right of preemption on D's share, he would buy such share leaving nothing to A. A and C employed many other tricks and artifices in order to void B's right of preemption.
A. Since C bought A's ground and gave away his own ground in partial payment thereof, he no longer owns the latter ground. Since a person who buys real property desired by an abutter, merely acts as the agent of such abutter (B.B. 108a), C must deliver to B the ground he bought from A, receiving in exchange the ground B bought from D plus a refund of his money. Were B unable to acquire such ground from D, he would have repaid C with money for the ground C gave to A; the value of such ground would have been determined by experts and not by C. C would not have been able to claim that his ground was very precious to him having for him the value of the "estate of Bar Marion", for such claim is valid only when a person is seeking to take away the property of another (in exchange of his own) against the will of the latter who may plead that his property is very precious to him. But in our case C has sold his property to A, and is only entitled to its market price. Moreover, even if the aforementioned sale were not concluded as yet, and an understanding merely existed between A and C that C convey his ground to A on condition that the conveyance of A's ground be without any interference on the part of the abutters, A could not have insisted on exchanging his ground for ground exactly similar to that of C. A could not have attached special importance to C's ground as having the value for him of the "estate of Bar Marion", for the reason already stated. Therefore, B would have been able to pay A with other ground, located in the same town, of equal value as that of C. Many persons have the erroneous notion that the preemptive right of an abutter is void whenever an exchange or real property is involved. Were this true, the parties to a sale of immovables would always add a small piece of ground to the purchasing price in order to place the transaction in the category of exchange of real property, thus turning into a hollow mockery the ordinance of the Rabbis who created the law of preemption for humane reasons. Therefore, whenever we suspect that the circumstances of a sale of real property were specially arranged in order to circumvent the law of preemption, we sustain the preemptive right of the abutter.
SOURCES: Cr. 193; Am II, 199, 200.