I am in NE Ohio, not far from you. I do a handful of apps for another company and I bill them (although I am required by law to leave certain info at the property that I am applying). I believe that they up charge on the cost to the customer but I do not know for sure or what amount. I am not crazy about the idea though because as far as that side is concerned it is my reputation on the line. I don't want to be known as over-priced.
My charges to them are my standard charges. I do not give a price break for them to make money off of my labor and my materials. I have worked hard to come up with good price points and they are what they are. I do fertilize the two owners yards as well. I think the benefit for them is they are able to offer full service to these customers that are looking for that. Also, I do offer full service lawn care and they know that I will not compete with them for their mowing. I just do the fert/squirt and aerating services. They don't push to offer these but when they are asked, they contact me. It seems like both sides are happy.