I work as a Mashgiach in a nearby restaurant and recently we switched from small produce supplied parsley to a Supermarket bought variety. We made this switch because it is a superior product at a similar price (I believe we get a discount from the Supermarket). Even though I spend nearly my whole day with those vegetables I have very little influence on that decision. These Supermarket vegetables (parsley, cilantro, and a few others) are a better quality product but are not anymore cleaner nor bug free. Now, except at Pesach, I never eat parsley at home so I can't really say if this is a fluke or not, but I doubt it.
The other Mashgiach there (different shifts) and I hate checking parsley as it is consistently the dirtiest vegetable and is always infested. The Vaad I work for requires the use of salt and/or vinegar (depending on the vegetable being checked) for the checking. Al Pi HaHalacha it is not necessary to use either of those but as long as you are not using that much it shouldn't hurt the vegetable. [The standard we use is that if you can taste the salt/vinegar in the water (before the vegetable is placed in the bucket) it is enough].
Anyway, the parsley. I hate parsley, even after two pre-washings and two bedikot I still find bugs and this is the Supermarket variety. So if you're not washing your vegetables well please do yourself a favor and start. I know you can't find commercially pre-checked parsley/cilantro, but after you've seen the bugs in vegetables that I see everyday (ugly ones that scowl at me) will always give your vegetables the checking they deserve.
Coincidentally, I find it interesting that the topic of shratzim is usually the last (if covered at all) topic in a Kashrut shiur. This is an issur d'oraita where many people are lax but are machmir on minhagim, but I don't think I'll ever understand them.