[BroJoeK]

Vigilanteman: "Their commanding officers forced them to return and either trade back or pay them the fair market value for the difference."

But "Fair market value" paid in Confederate currency was becoming increasingly a bad joke:

"As the war progressed, the currency underwent the depreciation and soaring prices characteristic of inflation.
For example, when news of the Confederate defeat at Gettysburg reached the public, the Confederate currency depreciated 20%.[3]
Confederate President Jefferson Davis asked private citizens to restore the value of the Confederate dollar by mutually agreeing to sell and buy items only at reduced prices.[4]
In October 1863, Confederate States Senator Louis Wigfall of Texas said that a Confederate soldier received $11 per month in pay, which was worth the same as $1 had been worth at the beginning of the war.[4]
In September 1864, one Confederate dollar was worth the same as three cents of United States currency.[5] "

Further, by the time of their third raid on Chambersburg in 1864, there was no discussion of "fair market value", but only demands for cash with threats to burn down Chambersburg if not delivered.
When the citizens refused, Confederates burned down Chambersburg.

[Vigilanteman]

Correct. The relatively gentlemanly conduct on both sides deteriorated as the war dragged on. Early in the war, it was commonplace to parole captured enemy soldiers.

The parole basically consisted of surrendering their arms, giving their name and other identification information to their captors and signing a document pledging not to take up arms again under penalty of death by firing squad. They would then get a travel document to return home and, were possible, rail transportation to the front.

Both sides honored the paroles at first. But, among other things, it became an honorable way to desert.

[rxh4n1]

But “Fair market value” paid in Confederate currency was becoming increasingly a bad joke:

Confederate money is back but we call them Bidenbucks.