Roman goddess of good faith and honesty, who oversaw the integrity of the Romans. She was closely associated with Jupiter, and her temple was built near his on the Capitoline Hill in 254 BC. In the later Roman period she was called Fides Publica ("Public Faith") and was considered the guardian of treaties and other state documents, which were placed in her temple for safekeeping
Someone's bona fides are their good or sincere intentions. Mr Perks questioned them at length to establish their bona fides. if you check someone's bona fides, you check that they are who they say they are, and that their intentions are good and honest