Thanks Mr Sparkle. I decided not to get that one I was looking at, I got a different one that seemed healthy (although he's really inactive since yesterday and I'm worrying...). He seems to have a missing ray(s) as well (I didn't notice until I got him home) although I'm not sure exactly how his fins are supposed to look (he's a crowntail, the short ray is at the front of his dorsal fin).
ha! I've already done 2 today, in case the fake plants are giving off chemicals or something..... I hope you are right about him being ok, he's just hanging in the water, not moving at all.... I stood there for ages comparing the fish and picked this one because he seemed the most lively and attentive and now he's just sitting there.