Sad as it is to say imo alot of SB fish are hard to prove... for the obviouse reason of getting x-rays ect of the vertebra for the prices they often change.. I wouldn't buy one w/out proof, also to see what kinda messed up the internal organs are... stunting is a common practice ( disgustingly unethical imo) and for what your pricing the fish against your Oscars I would bet against it being a SB. either its stunted, or a reg RTC in all likelyhood. But you never know. You could be lied to.. or the person with the cat may honestly believe it's a SB. I would ask about where he got it ect...
Hes tld me it's from my lfs. And gave me the name of the worker there as its his cousin. Called the lfs this morning and its confirmed to be an SB. As I've used the lfs for around 3years now and never lost a fish and always had great advise I went for it. He's hugely shy though been in 24 hours now and won't move from behind the rocks.