Only properly trained individuals are qualified to check for infestation-don't try it.

Mishnah Berurah in Hilchos Morer brings the Shu"t Chasam Sofer (130+-) that one must have "anushim-mi'yu'chudim-mi'su'yomim" with very good eyesight to inspect the lettuce, otherwise one may not use lettuce for morer.

Rav Shmuel Wosner, shlita says the chasam sofer is referring to special individuals that are experienced & it's known that they can find all of the camouflaged insects.