I see from your profile that you are located in Boston, a large northeastern city. This should make your seamstress search somewhat easier. I am located in Atlanta, another large city with no shortage of seamstresses.
Money is money and business is business, so I don’t think you are going to run into anyone who is going to turn your business away. In my area, strip mall dry cleaning shops often offer shoe repair, as well as alterations. Trouble is they send out their alterations work, after they do the marking and pinning up. I prefer a place that has a seamstress on the premises. Thus, search for a place that has an on site seamstress. Make phone calls. Somebody once told me there are seamstresses that operate out of private homes, but I am not sure about that.
What I did was locate a few places that had on site seamstresses, then I visited them in person while cross dressed and told them I had dresses and skirts I wanted to bring in and get altered and could they do the work for me? I wanted to see their reaction.
Keep in mind, seamstress work is not cheap. I just had a long dress shortened. It cost $25, and I am a long time regular customer of this particular lady. The dress was of light material.
BTW, I often bring in a dress when I am in male clothing. Then try it on in the shop and step out of the dressing room so the seamstress can fit it for me. It is so much fun watching the reaction of dry cleaning customers as they come in and see this guy in a beautiful dress with a seamstress doing a fitting.