In Massachusetts the home inspection is mandatory before you sign a purchase and sale agreement. I'm sure you could waive it, but you should not. At this time (2013) a home inspection costs around $500. Your realtor will probably suggest a home inspector for you. Even though your realtor is a buyer's agent it is probably wise to arrive at your choice of home inspector independently. Like picking any other service provider, you should put yourself in the position of an employer and do a short interview and get a feel for what the person is like. If you 'click' I would say pick that person. To get ideas about what to ask during the interview you can do a web-search for "picking a home inspector".
I did go through those websites to get an idea of what to look for, but when I phoned up the inspector I asked questions that I had when I toured the property I was looking at. So, I asked very specific questions about plumbing and electricity as I saw the fixtures in the house. I ended up going with a person I was on the phone with for 15min from whom I got complete, direct and easy to understand answers. At the end of the interview I made sure I got that person during the inspection and not some one else.
One thing that I did not expect was for the home inspector to give me maintenance tips about the house and clear explanations of why these tips were needed. This turned out to be very educational and interesting. You could add a question like "Will you take me through some brief tips about home maintenance while you do the inspection". Also, I made sure the inspector was OK with me tailing them and bombarding them with questions through out before I hired them.
Also, this was a little delicate, but I arranged that I could speak with the inspector in private, without even my buyer's agent in the room. The inspectors I spoke with all said that they did not care, their report would be the same regardless of who was in the room, but people can have subtle effects on behavior.