I have a law degree. However, the following is NOT legal advice.
In response to the question about the purchaser of such illegally-commissioned works, I note that in general in the law, the very best and most righteous holder of property is one who is a good faith purchaser for value without notice. I am fairly certain this applies here as well.
What does that mean? That means that if you purchase
a) in good faith -- without malice or an intent to trick anyone or commit fraud or do something bad AND
b) for value -- you properly paid a fair market value for the good (be it in $$$ or in trade) AND
c) without notice -- without notice that something was incorrect, without knowing what you were doing was somehow wrong, without knowing an item was stolen or otherwise shouldn't have been sold to you -- this includes things that AREN'T illegal to sell, like the coffee you buy in the morning, because, well, you had no notice that anything was amiss
then you are, by the law, almost 100% certainly always going to be the most appropriate person to hold absolute title to something that no one is able to take away from you.
(A few jurisdictions have variations for real estate, not important here.)
So, while I'm neither conversant on IP law nor officially a lawyer for a few more months, if you previously bought a commissionned item in the above manner (you paid a reasonable amount for it with a pure heart and had no idea at the time it was wrong), you shouldn't worry.
If anything lexxy or others report contradicts this, go with them.