Even with all upgrades bought, blackjack gave me negative. The one in this image is only -800 or so, but that's because I kept it a $1 so I wouldn't lose much. This is also after I let the game run over night.
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Other than the slow down around blackjack, it's really good.
Were you using the "Spy" strategy? In my tests it brings the win percentage up to 45%, but the increased return comes from the blackjack payouts, especially with the 2-to-1 blackjack upgrade.
The first time I lost, I was using the spy strategy. On the second time I played (the time I won), I don't remember. I think I was mixing it around to see if anything would work.
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