I bought 2 pieces in the past via chrono24, i think i can share a bit:
1. Chrono24 do offer escrow service, payment to chrono24 once u put order, payment go to chrono24 first, only when you received the watch as per advertise, you inform chrono24 for payment release to seller.
2. It mitigates scam for buyer as well as seller with their remittance service.
3. The buyer protection is a free service from chrono24: secured payment, insured shipping, dealer screening, authenticity guaranteed n etc.
4. They have "trusted checkout", where official receipt and certificate will be issued by chrono24 with watch spec to verify the watch authenticity.
5. I don't see many dealer or private seller in chrono24 accept paypal as chrono24 already offering their own escrow service with buyer protection. Paypal will add cost to seller that would pass back to buyer.
Hope the above helps, bought 2 GS in the past, both pawnshop and private seller in Japan. So far so good and all msg via chrono24 are captured, just remember NOT to accept the deal outside the system.