First of all, you will get a few dozen replies to your request, so see what they all say. If you really want to have fun, go into any seacost bar and ask out loud if there are any Realtors who could help you buy a house. You will not have to buy a drink for the balance of that evening...that's for sure.
I am a local broker in Stratham and Greenland. As it happens, I sold my real estate company and am in Florida for the winter, I will be away until Memorial day, so you probably will not be choosing me...but I do have a few dozen friends whom you might contact.
If I wanted to buy NEW CONSTRUCTION, I would start with Scott Gove. http://www.thegovegroup.com/
He is a friend and well known in the Seacoast. He owns the Gove Group and knows the territory, he has homes under construction now, and would start from scratch for you if that were your pleasure..
If I were thinking about an existing home, (and you know any Realtor can sell you any existing house) I would look for a good solid Buyer's Representative, someone who knows the area, the neighborhoods, schools and so on, and has long term contacts with banks and title companies. Probably you would want someone who was busy without being the County's top producer. If you are interested I would privately give you a short list--but not on this forum. Just reply to my web site.
Hope this helps,