The fact that gs even -sent- you his code to look at, which you say did work at least to a degree, says something right there, that's a pizza slice, even if you or he got an idea from the most basic, abstract underlying algorithm behind it. But that is trivial in the black and white world of simply breaking a deal. There is no gray area here.
GS complains he was unhappy with the quality, but he did not start the bug-report, feedback, bug-fix cycle that is inherent in the development process. Any developer knows this cycle is critical, and that the first draft of anything always has bugs. GS didn't pay up and hence didn't get his bug-fix cycle.
He broke his deal, weaseled his way out of paying, after stringing him along for months. Whether or not he used it is irrelevant, though if he is dishonest enough to break the deal, I wouldn't be surprised if the code is in there anyway.
I have to re-iterate this. From my personal experience, testDummy is not only an excellent programmer, he works hard and communicates well. He takes his work seriously. He delivers fast and surprisingly effective results. He's quick to fix bugs, make tweaks and all the while being friendly about it. With my project, he persisted, patiently, with my tweaks and little adjustments until I was satisfied. Not only that, I had a two week deadline for Dusmania when tD started-- and he worked night and day to get it delivered on-time. He stayed in constant touch with me the whole time. And it was on time. That's professionalism. Professionalism is also keeping your wordand paying your subcontractors.
To this day I am stunned with the results-- and some professional coder friends of mine who work for Rockstar and Doublefine couldn't believe this was done in 3DGS by just one guy in two manic weeks. Even his first drafts worked great.
Not only has gs cheated testDummy out of countless hours, he also slanders him here in the forum. There is no gray area here. tD is owed his money and at least an apology. Until that happens, gs' word is chaff upon the wind.