In our case, the comps were made on properties which sold and were of similar description, i.e., # of bedrooms, # of baths, square footage, garage, etc. Then they would up and down the price from your listing price. Like I said, the comps are only on recently sold properties in your area. We are somewhat rural and the comps were within the county.
When talking to agents, determine how she/he will market your home, i.e., newspapers, open houses, multi-listing. Determine how many properties have they listed and sold. If this number is high, look at the info two ways. Obviously, success, but also if they are extremely busy, how much effort will they put into selling your property. Find a realtor who is "hungry" and go with your "gut". Good luck.