How can Ethan pass as a trusted security engineer in Spain?

At the beginning of the movie, Ethan (Tom Cruise) is at the top of a pinnacle in Utah and receives his mission. He then has 48 hours to recruit thief Nyah (Thandie Newton). He does so by going to Seville, Spain in a rich mansion and creating an elaborate masquerade in which he's watching Nyah stealing a necklace, getting caught, and revealing himself as the security engineer of the place and the two of them completing a security test (https://www.youtube.com/watch?v=NvUZx-rhXMA). Now how did he do that. Did he forge a fake identity then created a trusty relationship with the owner of the mansion in two days? Is this an ongoing thing, like a summer job he goes to every few months between world-saving missions and he actually do security work there under another identity? If so, does he have a lot of jobs like that everywhere on the planet? Seems strange it was the one place Nyah was going to rob. Was this a complete setup and the owner/guards were on it the whole time? If so why would he secretly gesture her to grab her gear when they were getting caught? Wouldn't all of this made much more sense if he was wearing one of those fake rubber face so we could actually believe he was some trusted employee there?