My great grandmother lived at her uncle's inn near Lemberg, in Galicia. in the 1880s. I am writing a novel based in part on her experiences. Based on my research so far, it seems to me that her uncle would have had to "sell" the inn to a gentile before the sabbath and "buy" it back from the gentile afterward, every week, in order to profit from weekend traffic. It seems this was commonly done; whether everyone agreed that it was permissible I don't know, but apparently they did it. I am wondering if it would have been permissible for a gentile servant to perform this function. And also would a servant have been a shabbas goy too. In both cases, it seems like a stretch, since clearly the servant is obeying the instructions of her Jewish employer.
Yes and no. The Lubavitcher Rebbe writes exactly on this topic in Likutei Sichos, Volume 31, second parshas Mishpatim.
The non-Jew must keep the Sheva Mitzvot Bnei Noach. He is considered like a Ger Toshav eved/sachir. He must rest on Shabbat, but may do melachas for himself. He is not in the geder of shabbos goy.