the guy selling it says its 54cm but it looks a lot smaller to me. is it just me?

its a Novara Corsa ST

It looks 54 to me. I have a Raleigh and the distance between top tube and down tube at the front looks the same.

It looks 54 to me. Here's a 54 I just built up. The head tube lengths and proportions appear to me to be very similar.

I'm thinking 52. I just built two 54's, have another one on the rack, and I think it's smaller than them. On 50's the top tube and down tube basically touch. One finger in there is a 52, two fingers is a 54.