yeah, i hate that.  i recently ordered a bunch of sarco frags but got a mixture of lobo, sarco, and sinularia frags.  very similar in look though (these specific specimens) but a couple were obviously not sarcos even in their "frag/young state". (unless they are s. digitatum, which i highly doubt)
the yellows though are usually not a sarco they (ols) screw up on though because of the obvious coloration differences.  the worst i've seen "typical" yellow sarcos look was a brownish canary-yellow but it was because it was all ticked off and sick.  eventually it took a decent golden coloration.
care for the brownish types are just usually lower light intensity versus the yellows (high intensity lighting).  slightly higher flow seems to do them (browns) better than yellows ime.  all that's very general info though.  hth