
käuflich
available for purchase
Such that one can buy it; offered for sale.
Diese Software ist nicht frei verfügbar, sondern nur käuflich zu erwerben.
This software is not freely available, but only available for purchase.
available for purchase / corruptible
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available for purchase
Such that one can buy it; offered for sale.
Diese Software ist nicht frei verfügbar, sondern nur käuflich zu erwerben.
This software is not freely available, but only available for purchase.

corruptible
A derogatory term for a person who is willing to betray their convictions or act dishonestly for money; open to bribery.
Es stellte sich heraus, dass der Schiedsrichter käuflich war und das Spiel manipuliert hatte.
It turned out that the referee was corruptible and had manipulated the game.
The adjective 'käuflich' (available for purchase/corruptible) is derived from the verb 'kaufen' (to buy) and the ending '-lich'. It literally means 'buy-able' or 'something that can be bought'. This basic idea applies both to products and to the (negative) description of people.
Ist dieses Kunstwerk käuflich oder nur eine Leihgabe?
Is this work of art available for purchase or only on loan?
The meaning of 'käuflich' (available for purchase/corruptible) depends on whether it refers to a thing or a person. If it refers to a product, the meaning is neutral. If it refers to a person, it is strongly negative and means 'bestechlich' (corruptible/open to bribery).
Die Eintrittskarten sind ab Montag käuflich.
The tickets are available for purchase starting Monday.
A very common and somewhat formal combination is the phrase 'käuflich erwerben' (to purchase/acquire for money). It is often used in business language or official information.
Das Buch können Sie in jeder Buchhandlung käuflich erwerben.
You can purchase the book in any bookstore.
bought
When referring to people, gekauft and käuflich both describe dishonest influence through benefits. Gekauft means that the bribery has already taken place. Käuflich describes a person's general willingness to be influenced for money.

Der Schiedsrichter gilt als käuflich, weil er Bestechungsangebote annehmen würde.
The referee is considered corruptible because he would accept bribes.
Nach der heimlichen Zahlung galt der Schiedsrichter als gekauft.
After the secret payment, the referee was considered to have been bought.