Should I have a diagnostic done before buying a vintage watch?

[ron4]

Hello everyone! I'm thinking about buying a used vintage watch. It's beautiful and rare, but I'm unsure of its condition. I don't want to have to pay for expensive repairs after purchasing it. How can I tell if the mechanism is working properly without disassembling the watch myself? Are there any tests or services I can use to check it before buying? It's important to me that the investment is safe and the watch actually works. Has anyone encountered this?