i look for body lines or wall/door frame lines that should be straight, but are not in the photo
for example, in pic #1, the woman's left forearm (right side in the photo) should be a straight line. you can check it easily with the straight edge of a piece of paper. the outside surface of that arm has a distinct bend in it, approximately 4" below the elbow. this would be evidence that the narrowness of the waist has been enhanced by photoshopping (or she broke her arm during rough sex and never got it set properly). a really poor photoshop job leaves 'ghost' lines that are parallel to the lines of the photoshopped lines; however, these ghost lines have been cleverly masked as follows. the effects on the wall that the photoshopping would leave, have been masked by the fake 'bright spot' on the wall. that bright spot is a pretty good touch, but it doesn't match up properly with the line of brightness across the bed.
always look at the background for evidence of photoshopping. for example in pic #3, the line of the edge of the bed is clearly visible to our left of the model; however, in the space between her body and her arm on our right side of her body, that line has disappeared completely - suggesting that her waistline in that area has been enhanced
have a look at pic #2 and see what you can pick out - there are several features
as mel mentioned, the leolist sign can be photoshopped in. i mean they don't even need to use it now that leolist has quit verifiying photos - that's the first clue. however, the model is definitely holding something - see the placement of her fingers in pics# 2 and 3 - but the lettering on the sign could have said anything originally
in pic# 4, can you see the packing tape attached to the bottom of her near breast through the mesh shirt? i'm guessing it's holding up a very droopy breast so that it looks perky. or maybe even holding some sort of prosthetic device in place?