Its good to hear you like your City Sport cap. I have 4 of them and have found I dont wear any of my other caps anymore.
Mine have all been bought from a local shop so I was able to try them on before buying. The sizing has always been constant, I am a size 58 (7 1/8 in old money) and every one of their caps has been a perfect fit. so would have no problem trusting the sizing if I was to buy online.
The only problem I have is the local shop wont be getting any new stock until September so no new caps until then - unless I see something interesting online
You are lucky to have a local shop that stocks such great caps. The ebay seller I bought this one from isn't listing them as City Sport in the search criteria - they are selling them at a good price, but my cap wasn't wrapped in anything, just stuck inside a rather thin plastic satchel - cheap postage though and arrived in Australia from Britain in 7 days - I think if the cap had been damaged they would have refunded me, but still, a bag or some paper wrapped around it would have been a good idea. I'm amazed that these caps have been under the radar for so long, considering how appealing, well made and priced they are.