Just because Masters opted for free verse when he put this poem together, that doesn't mean that it abandons all poetic techniques entirely. We mean, if Masters wanted to totally get away from poetic conventions, he could have just stuck a bunch of frying pans and dryer lint together and called it his poetry collection.
But no, this poem retains a few poetic sensibilities, and those can be found primarily in Masters' use of sound. For example, what stands out most clearly is the use of onomatopoeia. In the first two lines, we hear a sound:
SEEDS in a dry pod, tick, tick, tick,
Tick, tick, tick, like mites in a quarrel— (1-2).
In fact, we hear the same sound over, and over, and over again: "tick." No, Masters' didn't have a keyboard malfunction. He really wanted to hammer that word into our brains by repeating it so much. Now, "tick" can refer to lots of things (this is our favorite tick), but in this case the word is used to mimic the sound of the seeds rubbing together in that dried pod. That's onomatopoeia at work for you, highlighting just how dry those suckers really are (and, by extension, just how lame the poems they symbolize are). We get a repeat of this sonic effect again in lines 16-17.
As well, Masters uses consonance for added emphasis, like when he lists off those fancy-schmancy poetry forms:
Triolets, villanelles, rondels, rondeaus,
Ballades by the score with the same old thought: (5-6)
Notice all those L, R, and S sounds in those two short lines? The sounds pile up here to underscore the overwrought, precious, and too-decorated poems that Petit was guilty of writing in life. These sounds repeat again in line 15, and become the sonic equivalent of a deep fried chocolate pie that's covered with Nutella and fried again before finally being frosted with chocolate cream. It's just too much, gang.
Masters, then, uses sound in the poem to call attention to the shortcomings of the kind of poetry that Petit was guilty of in his fictional life, and that Masters himself wanted to resist in his own life.