Chasam Sofer & Mishnah-Berurah state as some of the requirements for insect checking are;
Excellent eyesight (20/20).
Specially designated individuals = experienced & Yirei-Shomayim.
The average consumer does not meet the required criteria.
The only processor that meets the criteria, is the Positive Company Lab.
Therefore when kashrus certifiers tell you either wash very well under a strong stream of water, or soak, sponge, rinse etc. You may not use the product, as you don't meet the criteria.
Or the certifier tells you it's hard to check and of course you don't have the patience either, cut it in half & inspect for string that look like the parts of the fruit, etc, or break the buksa in small pieces & inspect & wash each small piece, etc. They are just fooling themselves & the consumer.
All kosher certified frozen strawberries requires a blending to a puree or cooking, regardless of the misinformation a kosher certifier may tell you.
They may be right in theory, but are not correct in fact.