They will low-ball you.
I used to be a real estate agent in Kansas City metro, and I have relatives that are investors. They will want to "flip" your house.
They will offer you very little, put some work into it (fresh paint, cosmetic work, new fixtures and carpet), and then charge the next guy thousands more than it is worth.
It is because of the real estate market being over-saturated with people like that that the real estate bubble burst a couple of years ago, resulting in increased bankruptcies and foreclosures.
So be careful.
Get your house appraised. Run some comps (house comparisons with similar features, etc.)
I don't know where you live or what your current house is like, but I could run some comps for you if you want.