One way to tell is to look at the tail piece. In most cases a trapeze tail piece will be on a hollow body and a stop tail piece will be on a semi-hollow body. Some semis might have a trapeze, but no hollows (that I know of) will have a stop tailpiece. What is impossible to tell until you really study a guitar in hand is if a guitar is truly hollow or has a sound post under the bridge area that reinforces the top underneath the bridge. Deep hollows - probably not. 2"/2.25"/2.5" depth guitars - maybe. My Gibson ES-390 and Epi Casino Coupe are thin bodies that are fully hollow.