Just use the UBB code generated for you for each image in the gallery, at bottom of gallery page in image details section. Paste one of the relevent size in your for sale post. I find medium generally works best in posts.

If images were taken on a iOS device, you may need to manually edit the file extension that you pasted in back to iirc .jpg - the forum software seems to generate a filename extension that does not match that of the image uploaded.

Meridian owner since 1992
Prime & PSU, Focal Elear headphones, Roon (ROCK 8Gi5 NUC), Explorer 1 & 2, F80. 200/203, various Sonos (via Roon).