The economic sanctions against Iraq were rapidly unravelling prior to the Second Persian Gulf War, which finally toppled the Saddam Regime, but you really have to look no further than the underground oil trade with ISIS during the years they occupied large portions of Syria and Iraq, or even the trade which goes on with the DPRK; obviously sufficient to keep the odious Kim family in power over several generations.
Russia is also currently under sanctions, which slows things down a bit foe President Putin, but Russia's economic problems are more tied to the lack of economic diversity (much of their foreign income is based on oil exports) and the internal kleptocracy, which siphons off wealth and investment capital to line the pockets of politicians and their favoured clients.
You could also look at the case of Iran, under sanctions for their nuclear program. In an interesting move, Saudi Arabia began flooding the world market with oil just prior to sanctions being lifted, in order to deny the Iranians new oil income, as well as to punish the Russians for supporting Iran. This strategy banked on the idea that Saudi cash reserves would last long enough for their enemies to collapse, but failed to take into account the innovative nature of the US oil industry and their ability to develop technology and techniques to prosper even under low oil prices.
So sanctions and sanction busting isn't a simple yes-no equation, and often there will be many outside influences which make or break sanctions as a means of exerting economic leverage.