
Gutter cleaning must be done to maintain efficient water flow and drainage off of your roof and away from your property. Properly cleaning the gutters will eliminate clogged gutters and down spouts, and the resulting water damage problems than can occur.
It depends on your tree cover, but typically once in the spring and once in the fall. If you have very few trees, you could go much longer than that. If you have many trees you may need multiple cleanings in the fall.
People on ladders need to have insurance. Don't take their word for it.
Gutter cleaning is a messy business. You want a guarantee that your yard, sidewalks, patio, deck etc....are protected from the slop and cleaned up after.
They will likely need to use your hose, but should have all the other equipment necessary including adequate ladder, tools, etc.