I recently purchased a vintage Tudor from a private seller on Chrono24. I mistakenly thought the protection extended to private sales (stupid). Had some concerns about the authenticity of the movement based upon an invoice from the seller's jeweler regarding routine repair of the watch.
Anyway, I held the payment while I had the watch looked at by a local watch shop. I was able to converse with the seller who was nervous about the delay.
The seller indicted to me that he would take the watch back if it was not authentic as advertised. In reality, he could have just waited it out.
It worked out (watch was legit), but I am not sure I would go private again without more certainty about the seller.
As an amateur watch enthusiast the ONE thing I am learning from this site and others is that buying vintage watches carries so many risks.
Going thru the various threads detailing the experiences of watch enthusiasts much more knowledgeable than me is a sobering education.
You are swimming in deep waters trying to secure a vintage 1950's UG chronograph from an international seller.....