It was somebody's brilliant plan to purchase hundreds of thousands of coins, without moving the price.
I'm not sure I'd call pirate's scheme from the beginning a "plan", but it was definitely someone taking advantage of an opportunity he was creating.
pirateat40 deleted most of his posts on here, but you may remember he was asking either bitlane or smoothie (or both?) who they were, over and over again. Not sure if it was here or in IRC, but if here, he's since deleted those posts and they both appear to have selectively edited a few parts of their own. I'm not sure why I can't find this info again, but I know I saw something along these lines in August of last year, shortly after the run up to $15 and crash back down to $8. I checked a few of the threads where I was certain it was posted and its not there anymore.
Also, don't forget the Vandroiy bet (though I honestly think that was less opportunistic and more a warning).
I can think of a number of different ways you could game pirate's moneyPak to BTC (or vice-versa) operation if you knew exactly how it worked (and especially if you thought it was also a Ponzi):
Step #1: Become his best anonymous customer.
Step #2: Become his best anonymous investor.
Step #3: Make promises from both.
Step #4: Abuse trust.
Step #5: Profit.
Glad I never really got involved, this post was about the extent of my contribution:
https://bitcointalksearch.org/topic/m.1024661I feel bad for those that lost money, but keep in mind there's a few folks in that thread, brunic & usagi, notably, that even wanted to ban dissenting speak or wanted people to flat out "shut up". This forum, at the time of BS&T, was actually quite hostile to folks even suggesting it was a Ponzi or moneylaundering scheme, under the impression that if it wasn't, it'd be destroying a legitimate business.
I don't believe pirate actually thought that he was going to run a Ponzi or was planning on it. I think he had a solid but small moneyPak-for-BTC business model that worked on the scale of thousands of dollars, worked less reliably at tens of thousands, and utterly failed at hundreds of thousands. I also think his willingness to work with anonymous individuals probably sealed BS&T's fate.