Some IWB hoslters are sturdier looking than others. Most of the modern designs are obvisouly not suited for "crossdraw" type wear, but several years ago it was harder to tell.
Before the advent of the paddle designe, several manufacturers had simple "Clip-on" belt holsters. Those clip-on attachments looked very much like the IWB clips.
Also, Uncle Mikes offerred at least one hoslter that had a belt loop and a clip, that was designed to be used as an either/or.