So, sorry about the preaching here, but it is very important for licensed members of the professional industry - or even all the unlicensed people as well, such as office staff - to avoid using the words "non-toxic" or "safe" when referring to any kind of pest control chemical. If your customers ask you to use non-toxic pesticides it would be important to discuss with them just what their perception of that term is, because all over the darned internet you CAN find references to non-toxic pesticides, references made by people ignorant of the facts and in many cases playing a dangerous game. I have read plenty of websites pushing boric acid, for example, as non-toxic, and this clearly is not the case. The word non-toxic cannot be in our vocabulary but we do need to help our customers understand why without scaring them. 

The fact is that MANY of the products we use have a very low relative toxicity, and many of these are then diluted to very, very low levels of active ingredient using water as the carrier, thus diluting that relative toxicity to a level that should have no chance of posing any hazard to them or their pets or family. All of this, of course, hinges on our use of these products in a proper manner and according to the Label directions. 

Some of the insecticides that have such a very low level of toxicity to vertebrates include growth regulators, and these are for fleas and roaches. Others may be plant-based active ingredients such as tree oils, mint oils, clove, garlic, Neem, and other oils, but these are still toxic at some level of exposure. However, many of them are also labeled for use in Organic production or labeled as "reduced risk" or "exempt from registration" materials. These may be what your customers are thinking of when they ask for non-toxic pesticides, but you still need to explain to them that while they are natural they still have a toxic level and must be used with care. A lot of people are hospitalized every year due to their exposure to excessive levels of clove in clove cigarettes, and yet because clove is "natural" they believe there could be no possibility of harm. 

If these customers do absolutely demand that you use Non-Toxic products then all chemicals are off the list and you are down to working with traps, sanitation, exclusion, habitat modification, and other steps of IPM, which should be part of any pest management program anyhow.