I recently had a window replaced in my house and still need a few more done. This in my story on a fewf issues you need to be prepared for when getting estimates and having a window installed.
Finding a quality company to replace my windows was the first step. I relied on two sources for finding installer to call. First is friends and neighbors. I asked around for references form people I trust that had good experiences. Then I went to Google to search local companies and read reviews.
I found two local installers that seemed like good businesses and called both for an estimate.
This is when I found about about all the options. Wood vs. Vinyl, sliders or double hung? There are a lot of options theses days.
Make sure to check local ordinances for any rules you must follow. My installer knew the neighborhood and informed us of fire codes that requires certain size opening. This limited the options we had for window types.
During this process it can be helpful to ask someone, a friend or colleague, their opinion on your window decision. A second opinion is usually a good thing.
My last recommendation is to make sure to set appropriate expectations as far as install times. If you need it done quickly you need to let the installer. know.