Sorry it is difficult to trust almost anyone in the trades. It is easier to do the work myself and not deal with strangers in and around my house. When I have to hire someone I tell them up front that I'll be checking every detail, pay extra to purchase the materials myself, and if they don't want the job - well good! I always fine someone who will work with me as I pay a bonus for that.
Depending on just how dirty the outside of your house is and on the house's size, there are two ways to approach this job. If you live in an average-size house, use a garden hose with a carwash brush attachment to bathe the big areas. For caked-on dirt, use a scrub brush or a sponge and a pail of warm water with a good, strong household detergent in it. Work from the top down, and rinse all areas where you scrubbed with water.