Can You Sell the Master Ball in Pokemon FireRed?

No. You cannot sell the Master Ball in Pokemon FireRed.

If you try to sell it at a Poké Mart, the clerk refuses to buy it.

The same rule applies in Pokemon LeafGreen.

Why This Feels Unusual#

Most regular items in the bag can be sold at a Poké Mart. The Master Ball, however, is treated as one of the limited items in Pokemon FireRed, which is why the game handles it differently.

For example, other Poké Balls such as Great Balls or Ultra Balls can be sold normally.

Because of this, some players assume the Master Ball might also be sellable.

However, the game treats the Master Ball differently.

What Actually Happens#

In Pokemon FireRed:

The Master Ball appears in the Poké Balls section of the bag
It shows a quantity like other balls
However, Poké Marts refuse to buy it
The shop clerk simply says that the item cannot be purchased

Even though it is stored with other Poké Balls, the Master Ball cannot be sold.

A related question is whether more than one Master Ball can be obtained in the same playthrough.

In Short#

The Master Ball cannot be sold in Pokemon FireRed.

If you attempt to sell it at a Poké Mart, the clerk refuses to buy it.