Okay, thanks. Let me see if I can break this down for you.
with Y to have Z perform services on behalf of X. When Y agrees intermediate between X and Z, Y becomes X's agent. An agency relationship creates a duty of loyalty, good faith and fiduciary in Y toward Z. Breach of the duty makes Y liable for any damages sustained by X.
Here, X never paid Y for any services as agent, nor for any charges sustained by Y in pursuit of the agency on X's behalf. Therefore, while X has a theoretical claim against Y, without any damages, there is nothing to claim, and so the most that a court could award X would be nominal damages ($1.00).
However, were X to have some impending deadline to meet, whereby damages would be sustained were Y not able to deliver Z's services promised as part of the agency, then X would have a damage claim against Y, for breach of loyalty, because by destroying the result of Z's services, Y has definitely breach his/her duty to X.
The defense that X has not paid for Y's services may or may not prevail. The issue would be as to the intent of the parties in the creation of the agency, and that intent is not entirely clear. This makes for a very fact-centric litigation, and that means a trial, and trials are expensive (though we're probably talking about small claims court, because of the claim amount (less than $5,000.01). So in this particular case, the expense of a trial is trivial).
The issue of whether or not Y can charge X for his/her costs in paying for the retouch and then destroying the results, will likely be resolved in favor of X. The reason is that Y had a valuable asset (at least valuable to X), and Y unlaterally chose to destroy that asset. Consequently Y paid for the asset, and destroyed it. None of which will be charged to X. Had Y sued X instead of destroying the photos, then the court would have awarded X damages, because of the breach of contract in failing to pay. But, the destruction of the consideration
/photos, prevents X from obtaining the benefit of the bargain of agency, and once that occurs, X will be discharged from the obligation to pay.
Given all of the above, if your goal is to get paid for the retouch, then you need to have your artist send you another digital copy of the photos so that you "stand ready to perform" in the event that X actually pays you. The theory that you can charge X double for the service after you destroyed the first set of photos will not survive careful inspection by a competent jurist/judge.
I have a judicial temperament and my analyses rarely fail to play out similarly in the real world -- because I don't advocate one side's position over the other -- I just "calls em' as I sees em'!" So, while I realize my findings and conclusions here may not completely satisfy your need for justice, I would be willing to bet that if this matter ends up in a courtroom (which I somewhat doubt that it will), that the result will be pretty much as I describe.
Please don't shoot the messenger. Better to know that a dark alley is a dead end, before you turn into it and slam into the side of a building.
Hope this helps.