I can help with the communication since I am the largest (german) retro seller at Kleinanzeigen. All at your own risk of course. But seller seems legit and trustworthy at first glance... here is the translation of the item description:
Selling a beautiful steel classic:
NOS Yeti FRO F.R.O frame
Frame size of 48 cm C-T
I would describe the frame as NOS; a headset and a rear wheel were probably already mounted.
No cracks or dents visible.
The paint is grey-green and only minimal signs of storage are visible.
The number "500" can be seen on the underside of the bottom bracket housing, otherwise I couldn't find a frame number.
As a private seller, I exclude liability for material defects within the scope of the statutory provisions!
PRIVATE SALE WITHOUT WARRANTY AND RIGHT OF RETURN.
I will send the frame to Austria and a viewing or collection in Wiesbaden can be organized if necessary.
It is a fixed price.