This could honestly be anyone, not just e-liquid vendors who manufacturer from the convenience of their home. I'm sure there are some less than spotless mix labs, just as I'm confident that there are some less than clean items at the farmers market every day/weekend; I'd go as far as saying some items sold are questionable based on appearance and aroma.
At the same time, there are less than clean chain kitchens which are monitored by the Health Department, yet we still end up seeing old meat, rotten produce, hairs in food, etc. I've worked in the food industry and managed quite a few restaurants, even retail. Trust me when I say that it's easy to sway the HD away from what you don't want them to see, especially if you walk with them during their review. I've seen many a Store Manager do it. What would normally be a 85-88, which is pretty nasty (to me), come out as a 93-96+, which to the public eye, is good (but actually leaves room for many "critical" errors, ranging from food off-temp, which is dangerous, to improper storage, such as raw meat above cooked in the cooler).
If you eat out *anywhere* then you've been dealing with the "fat, sweaty, hairy dude" that chugs beer on a dirty couch for long long time. Restaurants are known for high turnover and the majority are not overly picky about who they hire as long as you can do the job you're applying for.
Just to give you an example. I used to bartend at a Chili's when I was 18 (11 years ago). I cooked for them here and there and really enjoyed it, until my Store Manager came by to help me on a really busy day, slapped a piece of chicken on the grill with his bare hands, turned it over and when he grabbed it with the tongs, dropped it into the trash can beside me. It was empty-ish and he said it was still good and that the grill would sterilize it in a few seconds, or we could deep-fry it and that'd take care of it. I told him no, and walked off and later quit.
Unless you can see everything that's happening in the kitchen, you have *no* idea what IS happening, and even if you could, you'd still miss a lot.