When buying Cavalry badges the following are give aways as fakes: KDG - The 1898 to 1915 pattern - a very common copy but the fakes come with 2 lugs on the scroll (rather than at chest level or on a slider)...
I've noticed quite a few 'S.A.S. / S.B.S.' T-shirts for sale on EBAY and here's some useful info, before you part with your cash: don't - it's a rip-off. Out of 50 shirts you'll see, maybe 2 are as issued...