Buy the best juicer you can afford. Domestic juicers usually retail between 25 and 50. I believe that it's healthier to juice non-organic produce than to not juice at all.
Pollution is the scourge of our age but fear is more crippling.
All bruised and damaged parts are to be removed before chopping. Pears are the most hypoallergenic of fruit, good for a delicate digestion with low fruit tolerance, juice in small quantities. Some Naturopaths use curative juices including potatoes to treat stomach ulcers. My advice would be not to use potatoes without naturopathic advice. I remove vegetable tops because they are soily or sandy and bitter.