You must do your homework before you buy any vintage watch from anyone.
My real experience:
1. Must go to the shop to see the watch physically. The website photos are so blur.
2. The movement model can even change when you see it physically (different from the website photos).
3. Your homework is utmost important when case no.2 happen. I normally will ask the "real" reason. But you own source of homework information will determine the authentication.
4. If you have doubt, just ask them to close back the case back , stop the purchase , and check with shifu or information again.