Which other scientists are you referring to, specifically? Link to source would be nice, thanks.

As for the staring effect: http://www.sheldrake.org/Articles&Papers/papers/staring/

See especially http://www.sheldrake.org/Articles&Papers/papers/staring/pdf/artefacts_elim.pdf and http://www.sheldrake.org/Articles%26Papers/papers/staring/pdf/sensoryclues.pdf about elimination of possible artefacts. Tests have been carried also blindfolded to eliminate what I guess you are suggesting, somewhat confusingly as I fail to see the connection to Sheldrakes controlled methodology. Closed circuit TV test, according to Sheldrake, show that "This conclusion is confirmed by an independent series of experiments in which subjects were looked at through closed circuit television (CCTV), while their galvanic skin response was recorded continuously, as in lie-detector tests . In these experiments, the lookers and subjects were in different rooms, and the subjects could not have received any clues about when they were being looked at through normal sensory channels. The subjects in these CCTV experiments were not asked to make conscious guesses about when they were being looked at or not; their physiological responses were unconscious. Yet there were significant differences differences in their skin resistance when they were being looked at on a TV monitor in another room (Braud, Shafer and Andrews [1990], [1993a], [1993b]; Schlitz and
LaBerge [1994], [1997]; Wiseman and Schlitz [1997])."

On the other hand Muller et alii CCTV experiment http://www.uniklinik-freiburg.de/iuk/live/forschung/publikationen/StaringEDAconsciousPA2006.pdf with very different methodology from "either-or" conscious guessing of Sheldrake et alii don't show PSI effect. They admit the sample data is very small to draw statistical conclusions.
And as such their very different methodology does not refute the results of other methodology, just raises further questions.

The main counter argument that the strong effect of study paradigm by Sheldrake et alii is product of guessing strategies remains AFAIK just a guess, as I'm not aware of empirical studies making clear what these strategies exactly are and how exactly they work to produce the strong positive effects.