These indulgences not only bestowed pardon for sins committed already, they were used to license the commission of future transgressions as well.
I was very interested when I read this, as it’s truely out of whack - so I did a bit of reading and found this: from New Advent:
History presents few characters that have suffered more senseless misrepresentation, even bald caricature, than Tetzel. “Even while he lived stories which contained an element of legend gathered around his name, until at last, in the minds of the uncritical Protestant historians, he became the typical indulgence-monger, upon whom any well-worn anecdote might be fathered” (Beard, “Martin Luther”, London, 1889, 210). For a critical scholarly study which shows him in a proper perspective, he had to wait the researches of our own time, mainly at the hands of Dr. Nicholas Paulus, who is closely followed in this article.
In the first place, his teaching regarding the indulgences for the living was correct. The charge that the forgiveness of sins was sold for money regardless of contrition or that absolution for sins to be committed in the future could be purchased is baseless. An indulgence, he writes, can be applied only “to the pains of sin which are confessed and for which there is contrition”. “No one”, he furthermore adds, “secures an indulgence unless he have true contrition”. The confessional letters (confessionalia) could of course be obtained for a mere pecuniary consideration without demanding contrition. But such document did not secure an indulgence. It was simply a permit to select a proper confessor, who only after a contrite confession would absolve from sin and reserved cases, and who possessed at the same time facilities to impart the plenary indulgence (Paulus, “Johann Tetzel”, 103).
As much cannot be said about his teaching regarding indulgences for the dead. The couplet attributed to him –
As soon as the gold in the casket rings
The rescued soul to heaven springs,
like that attributed to Luther,
Who loves not wine and wife and song
Remains a fool his life long;
though verbally spurious, can in both instances be in substance unfailingly traced to the writings of their respective authors. By Tetzel they are substantially acknowledged in his Frankfort theses. Here he accepted the mere school opinion of a few obscure writers, which overstepped the contents of papal indulgence Bulls. This opinion found no recognition but actual condemnation at the hands of authoritative writers, and was rejected in explicit terms by Cardinal Cajetan as late as 1517-19. By the teaching he laid himself open to just censure and reproach. **To condition a plenary indulgence for the dead on the mere gift of money, without contrition on the part of the giver, was as repugnant to the teaching of the Church, as it violated every principle of elementary justice. “Preachers act in the name of the Church”, writes Cardinal Cajetan, “so long as they teach the doctrines of Christ and the Church; but if they teach, guided by their own minds and arbitrariness of will, things of which they are ignorant, they cannot pass as representatives of the Church; it need not be wondered at that they go astray” (Paulus, “Johann Tetzel”, 165). It was this deviation from the correct teaching of the Church and the obtrusive and disgraceful injection of the treasury chest, that led to abuses and scandals reprobated by such contemporaries as Cochlæus, Emser, and Duke George (Paulus, op. cit., 117-18). “Grave abuses arose; the attitude of the preachers, the manner of offering and publishing the indulgences aroused many scandals; above all, Tetzel is in no way to be exonerated” (Janssen-Pastor, “Geschichte des deutsch. Volkes”, 18th ed., Freiburg, II, 84). **
If Tetzel was guilty of unwarranted theological views, if his advocacy of indulgences was culpably imprudent, his moral character, the butt of every senseless burlesque and foul libel, has been vindicated to the extent of leaving it untainted by any grave moral dereliction. These would hardly be worth alluding to, did not some of them have Miltitz as the source. But Miltitz has been so discredited that he no longer carries historical weight. “All efforts”, writes Oscar Michael, a Protestant, “to produce Miltitz as a reliable witness will prove futile” (Münch. Allg. Zeit., 18 April, 1901). “The circulated reports of Miltitz about Tetzel deserve in themselves no credence”, writes another Protestant author (ibid., 14 March, 1910).
The charge of embezzling the indulgence funds is also legendary. The precautions adopted to safeguard the alms were of a character that precluded all chance of misappropriation. The chest to receive the money always had two or three locks, the keys of which were in the custody of different persons, including a representative of the banking-house of Fugger. It could never be opened save in the presence of a notary. The ecclesiastical injunction was that the faithful had to deposit their contributions in person. To give it to the confessor or indulgence subcommissary invalidated the indulgence (Paulus, op. cit., 76-77). The Tetzel indulgence chests exhibited at Jüterbog and other German towns, are counterfeits, according to the Protestant writer Körner (Tetzel’s Leben, 73). The latest Catholic biographer of Luther, Grisar, writes: “To ascribe to the unhappy monk the ‘cause’ of the entire apostasy that set in since 1517 . . . is an untrue legend” (“Luther”, Freiburg, 1911, I, 281).
It seems like he has been misrepresented by protestant historians to a degree, and where he was wrong, the church did not support him. Seems fair enough to me.