Your local retailer is poorly educated then unfortunately. I hope it's a junior sales man newbie mistake. Gaziano & Girling ready to wear and made to order are what is often referred to as bench made, so although there is a lot of manual labor involved in the production they are actually machine welted. There is no difference in production technique for RTW and MTO although MTO seems to have a slightly better finish most of the time. The only shoes from G&G that are hand welted are the bespoke ones and these start at about £4000.
I know G&G experimented with making a line that was hand welted, kind of between the normal MTO or Deco line and bespoke but I think it's stuck at Beta stage (or even Alpha).