My advice is to do a few Google searches for real estate, homes and/or Realtors in Onset, MA and see who you find in the first 3 pages. (Some of the national comapnies as well as aggregators may very well dominate the 1st page). Also look at the "paid" ads in the right column for 'Relevant' ads for your marketplace. Then, check your local news papers (many STILL advertise in print), Look at sites like Realtor.com, Trulia and others and see who is enhancing their listings (they are the ones that are staying 'current') and finally drive around the area looking for Signs (that are not buried in the snow). Soon you will get a feel for who the 'players' are in your marketplace. Identify 3-5 of them and contact them for an interview/market analysis. Chances are you will find that most are within 'market range'.
Things to look out for:
Don't be swayed by someone trying to 'Buy The Listing' by giving you a higher price than the rest.
Ask questions, and ask the agent to Verify any stats or other info they pass by you.
And although the 'Firm' is very important, check the Agent's credentials (as the agent directly controls your transaction).
This may take a week or two to go through the process, but after interviewing 5 of the heavy hitters in your area, it should come clear as to who to hire.
On the other hand, you can try to sell it yourself (i.e. no real estate agent). However, like most, you will go through the process above - just a few months later.