While the wizard researched and prepared the great spell, the laundry owner schemed. He did not want to have to pay the wizard one bald groat let alone the fee demanded.
He decided that once the wizard’s usefulness was expended, then would he be killed. The laundry owner threw a feast in the inn and as well as all the villagers,
He gathered a band of desperados. All were wined and dined lavishly (at least in the laundry owners eyes). At last word came through to the laundry owner that the wizard was on his way to collect his fee. "Huh!" thought the laundry owner, "He was going to stiff me - nothing's changed!"
Just as he thought that "Parp!". "Parp, parp!". Soon the whole room was echoing to the sounds of "Parp, parp, paaarrrrrrrrp, groan".
The stench was astounding. In walked the wizard with a peg on his nose. Obviously he had anticipated the results of his handiwork.
With his own stomach roiling, the laundry owner said to the wizard "What have you done? Paaaarrrrrp!"
"I realised that whatever I decided to do to help you, you would try to evade paying me my just reward. In fact I suspected that you would probably try to have me killed."
"In this case I thought I would kill 2 birds so to speak and provide a solution to your woe and incapacitate whoever you had hired."
"You now owe me 1000gp" said the wizard who sat to await his gold. "Yes but precisely what have you done to us? p-p-paaaaaaaarrrrrrrrrrrrrrrrp!" wailed the laundry owner.
"Why I simply imbued all the salt in the village with the properties of Epsom salts and senna pods." Grinned the wizard. "By doing this I have negated the wish because you are all creating a magically induced stinking cloud!" So saying he smiled smugly and took his pipe out of his robe. It took three tries, but he managed eventually to get it to light using his magic. Unfortunately, the consequence of this action only took three nano-seconds.
Kwablewie-boom.