Then you can have fun measuring the pictures on eBay and use a known length such as chainstay to work out seat tube length. I use to do this on catalogues all the time so I could work out what the bike would look like as a smaller size as I’m only 5’ 7” and they always seemed to show medium sized frames.
My guess is 18”. They have nice short head tubes which makes it look smaller than it is. Have fun measuring!
They might not let it go for that much. Who knows. I’m sure they were after a lot more. They could have at least had the M&S the right way around in the title!