If a deal looks too good to be true, it may just be. Money managers at Goldman Sachs bought $2.8 billion face value of Petroleos de Venezuela bonds at a deep discount last week, attracting the ire of critics of President Nicolas Maduro. Investments aren't necessarily moral choices, but they can hit reputations.

Venezuela could, on paper, be one of the soundest emerging-market credits given that it has the world's largest oil and gas reserves. But the economy has been in precipitous decline since Maduro succeeded the late Hugo Chavez in 2013. Output has fallen by nearly a third over the past three years and inflation is projected to exceed 1,000 percent by the end of this year, according to the International Monetary Fund. Bare shelves and angry protests, met with violence, have become the norm.