Firstly, sorry for the delay in responding, my browser kept closing down everytime I tried to post so I'm having to use a diff browser.
Well I saved him, I know the shop won't change conditions, so I'll just have to keep going in and moaning and saying rather loudly "well isn't that just cruel" etc. Thing is the other fish are all well looked after and seem happy and healthy, I think it's a case of they haven't got room for lots of individual tanks for bettas so just stick them in with whatever and hope for the best.
My stats aren't fantastic so I decided to put him in with my corys in their 50L until I can get nitrite, ammonia etc down, they haven't bothered with him and vice versa so fingers crossed he'll be ok in there until his tank is ready. He seems alot happier and is swimming and eating fine
I've named him Koroshiya
I know it's not ideal rescuing him and lining their pockets but to me saving a life is worth more than proving a point.