What do you think of my child's dentist report?

I have always thought of dentists as used car salesmen. It seems everytime you go to get a cleaning, they find "something" that HAS to be done and they set your next appt. for fixing these things without even asking if it's ok..that said..I took my 8 year old for her cleaning to a new pediatric dentist. The dentist says "She has two cavities and she needs sealants on the other two back ones." Then they are shoving an orthodontist appointment on me even though they said they would probably just "take a look" because of her "crowding". Then they have me sign a release form for her "laughing gas" that she will NEED to have her teeth filled. She hasn't had ANY pain and these "cavities" they say need filling you can hardly see at all. I feel like they are just trying to make $! I hate to put my 8 yr old through this if it's not nec? I've never had cavities, so maybe I just don't understand. Shouldn't you wait til there IS a problem before doing alot of ging and drilling on a child?