From Chukei Chaim Part One:
Usually, a kashrus agency’s hashgachah only covers items in the store. Once a product leaves the store, e.g., in a delivery, the agency no longer takes responsibility for it. If the deliveryman is a non-Jew or a secular Jew and the product is not properly sealed, there can be kashrus problems.
The Badatz Eidah Chareidis states that its hechsher on produce stores, fish, pizza, etc. only covers items sold in stores displaying a valid certificate. Once a product leaves the store though, e.g., in a delivery, it takes no responsibility unless the store has an arrangement with the Badatz for that (מדריך הכשרות תשפ”א עמ’ 128).
One must be extremely careful about this with chains of stores that sell identical products, e.g., pizza, when one has a high-level hechsher and another has a low-level one. When ordering, one must find a way to verify that the pizza is not from another branch with a lower hechsher – there are true stories where this has happened.
From Part Two:
All Ingredients Badatz
Many people make homemade food products, e.g., mezonos foods for kiddushim, cakes, potato kugel, Yerushalmi kugel, herring, chickpeas, p’tcha/gala, dips, salads, fruit platters, chocolates, etc. They put a sticker on the package that says “All ingredients Badatz” and sell their products in stores, makolets, or mikvaos, or deliver them directly to customers. People rely on this, thinking, what could be the problem if all the ingredients are Badatz?
Common Shailos
Hafrashas challah. In every home kitchen, shailos come up; any posek who answers these types of questions all day can attest to this. Not infrequently, we are asked questions about foods made and sold from homes. For example, one woman who made sponge cakes for kiddushim had no idea she was supposed to do hafrashas challah after baking a certain minimum amount, because when they are made in small amounts for personal consumption, there is usually not enough flour to require hafrashas challah. This caused a pitfall: people enjoyed the mezonos with ‘all-Badatz ingredients’, but it turned out they ate tevel.
Fleishige keilim. Oftentimes, people use fleishige pots and utensils to make parve food, or they cut onions or garlic with a fleishige knife, such that lechatchilah, the food may not be eaten with milchigs. Because the food is parve, customers do not know they cannot eat it with milchigs. If there was some sort of supervision, the rav would ensure that only parve utensils designated for the food being sold are used.
Checking for bugs. We know that many fruits, vegetables, and flours often have bugs, even if all the ‘ingredients are Badatz’. If one does not know how to properly check each fruit, vegetable, and type of flour, he is likely to transgress the issur of eating bugs. It does not take much effort to check for bugs when making a small amount of food for the family, but when making a large amount to sell, it takes a lot of effort. There is a chance that, due to pressure, the person making the food will be lax; if there is supervision from a rav who gives instructions, it is likely the person will check better.
Heaven help us!