Moles are considered nuisance wildlife and in some states no special license is required to trap them. For example, in Missouri & Arkansas no special license is required to trap them. In Kansas a simple test is all that is needed to get a permit. Other states may have their own regulations regarding nuisance wildlife. Keep in mind that moles are insectivores and not rodents and poisoning is relatively ineffective. In some states it is legal to poison rats and mice but illegal to poison any other animals.
Also, moles do not live in "colonies" as some believe. Moles are solitary animals creating and living within their homerange. Just one or two moles can create a significant amount of damage giving the impression that there are more.
As far as mole control as a business it is a niche business that is in great demand in various parts of the country. As in lawn care you have a group of clients that take pride in their lawn and realize that it is an asset. They have invested heavily in sod, landscaping, irrigation and maintenance and don't want moles destroying it. Just like lawncare you are providing a needed service that the customer is willing to pay for. There are various service plans that can accommodate most customer's needs and as you build your client base each year you receive service requests from both new and previous clients. Just do a quick search for "mole removal", "mole control" or "get rid of moles" in your area to enlighten yourself a bit more on this type of service. With mole trapping and removal you are able to set your own schedule - rain or shine. Also, some of the peak trapping times are during your slow times so it helps supplement your business. As you build your route you are generally checking your traps every 5-7 days. This should coincide with your mowing schedule. The more traps you have set the greater the percentage of mole captures. So, if you have customers with mole damage you can profit from it or give the money away and refer it to an area mole trapper - like me!