We provide three detailed case studies of vulnerabilities in smart contracts, and show how property-based testing would have found them: 1. the Dexter1 token exchange; 2. the iToken; 3. the ICO of Brave's BAT token. The last example is, in fact, new, and was missed in the auditing process. We have implemented this testing in ConCert, a general executable model/specification of smart contract execution in the Coq proof assistant. ConCert contracts can be used to generate verified smart contracts in Tezos' LIGO and Concordium's rust language. We thus show the effectiveness of combining formal verification and property-based testing of smart contracts.