I met a customer at the San Francisco alterations tailor I work with the other day. Franz took a look at my friend, noticed that his jacket lining was hanging down in back, and immediately asked him for his coat so he could fix it. That is the kind of attitude a man needs in his alterations tailor.
We were at Franz Custom Tailors (166 Geary Street) because I have clothes for customers made in New York and fitted in either New York or San Francisco. We needed the sleeve length adjusted on a new jacket, sleeve buttonholes sewn, and, surprisingly, the quarters opened a bit. All these things Franz does very well.
To my mind, the best alterations tailors should be completely competent to make a jacket. Not cut the cloth mind you, but they should be able to perform most if not all of the operations required to make one. That said, I prefer that they make no claim to be a custom tailor, as I think the two are oil and water. If a tailor wants to make suits, he should make suits and forget about making alterations.
Finding an alterations tailor is not a difficult task even in the relatively tailor-free zone that is the United States of America. Go to the best men's store in the area and ask where they send their alterations when they are too busy to handle them all in-house. If they speak well of a place, pay that firm a visit. Here, first impressions count. The premises should be clean and organized, or the work will not be.
That established, talk to the proprietor. A tailor does not have to be a friend but he or she should listen well, communicate clearly, and volunteer a price and a completion date for each job in advance. I may not be representative but I see Franz several times each month, and those little things matter.