Non-Jews are assumed to be Noahides by Jewish law
The opinions of a few of the noted and authoritative scholars are here cited to show the change in halacha towards non-Jews and the assumption whether they are idolators or Bnei Noach, since post-Talmudic times.
From the Post-Talmudic Period to the Present Time
R. Sherira Gaon, president of the college in Pumbedita in the tenth century, permitted Jews to bring suit in a Gentile court on the defendant's refusal to have the case adjudicated by a Jewish tribunal. "Even if the Jew be the robber and the Gentile the one robbed, it is the duty of those who know it to so testify before the justice" (quoted in "Be'er ha-Golah" to Shulḥan 'Aruk, Ḥoshen Mishpaṭ; see also ib. 426, 5).
Maimonides (twelfth century), in his code written in Egypt, says: "It is forbidden to defraud or deceive any person in business. Jew and non-Jew are to be treated alike. If the vendor knows that his merchandise is defective, he must so inform the purchaser. It is wrong to deceive any person in words, even without causing him a pecuniary loss ("Yad," Mekirah, xviii. 1). In his Mishnaic commentary Maimonides remarks: "What some people imagine, that it is permissible to cheat a Gentile, is an error, and based on ignorance. The Almighty—praised be His Name!—instructed us that in redeeming a Hebrew servant from the services of a Gentile owner 'he shall reckon with him that bought him'" (Lev. xxvi. 50), meaning to be careful in his calculation not to cheat the Gentile. This was in Palestine, where the Jews had the upper hand over the Gentiles. How much more should the law be observed at the present time, when they have no sovereignty over the Gentiles. Moreover, neglect of the precept would cause the desecration of His Name, which is a great sin. Deception, duplicity, cheating, and circumvention toward a Gentile are despicable to the Almighty, as "all that do unrighteously are an abomination unto the L-rd thy G-d" (Deut. xxv. 16; commentary to Kelim xii. 7).
Moses of Coucy (thirteenth century) writes: "I have been preaching before those exiled to Spain and to other Gentile countries, that, just because our exile is so prolonged, it behooves Israel to separate from worldly vanities and to cleave to the seal of the Holy One, which is Truth, and not to lie, either to Jew or Gentile, nor to deceive them in the least thing; to consecrate themselves above others, as 'the remnant of Israel shall not do iniquity nor speak lies.' . . . Behold, the visitation of the Flood for the violence done to the wicked Gentiles!" ("Semag," § 74).
Opinions of Jewish Scholars
About the same period R. Judah of Ratisbon, compiler of the "Sefer Ḥasidim," quotes: "It is forbidden to deceive any person, even a Gentile. Those who purposely misconstrue the greeting to a Gentile are sinners. There can be no greater deception than this" ("Sefer Ḥasidim," § 51, Frankfort-on-the-Main, 1817). "If either a Jew or Gentile should request a loan, he should get a frank answer. Do not say, 'I have no money,' when the reason is the fear to trust" (ib. § 426). "One shall not act in bad faith even to Gentiles. Such acts often bring down a person from his rank; and there is no luck in his undertaking. If perchance he succeeds, punishment is visited on his children" (ib. § 1074).
In the fifteenth century R. Isaac b. Sheshet, who lived in North Africa, in response to an inquiry regarding the status of a non-Jew, quotes authorities to prove that the Gentiles nowadays are not ultraidolaters, and consequently are not subject to the Talmudic restrictions mentioned above. He further says: "We must not presume that such restrictions were fixed rabbinical ordinances, not to be changed. On the contrary, they were made originally to meet only the conditions of the generations, places, and times" (Responsa, No. 119).
Rabbi Yosef Caro (sixteenth century), the author of the Shulḥan 'Aruk, decides that "the modern Gentiles are not reckoned as heathen with reference to the restoration of lost articles and other matters" (Bet Joseph to Ṭur Ḥoshen Mishpaṭ, § 266; see also Ṭur Yoreh De'ah, § 148, ed. Venice, 1551).
Rabbi Benjamin Beer (seventeenth century), replying to an inquiry regarding an error of a Gentile in overpayingeighteen ducats, says: "For the sake of consecrating the Holy Name, a Jew shall correct and make good the error of a Gentile. . . . Jacob charged his sons to return to the governor of Egypt the silver put, perhaps by oversight, in the sacks of corn purchased by them from him. One must not take advantage of an error made either by a Mohammedan or by a Christian. Otherwise, the nations would rightly reproach the chosen people as thieves and cheats. I myself had occasion to restore to a Gentile money received through error" (Benjamin Beer, Responsa, No. 409, Venice, 1539).
Rabbi Eliezer of Mayence writes: "The commandment prohibiting theft, like those against murder and adultery, applies to both Jews and Gentiles" ("Sefer Ra'aban," § 91, Prague, 1610).
Rabbi Ezekiel Landau (eighteenth century), in the introduction to his responsa "Noda' bi-Yehudah" (ib. 1776), says: "I emphatically declare that in all laws contained in the Jewish writings concerning theft, fraud, etc., no distinction is made between Jew and Gentile; that the titles 'goi,' akkum,' etc., in no-wise apply to the people among whom we live."
Rabbi Shneur Zalman of Liadi (d. 1813), the representative authority of the modern Ḥasidim, in his version of the Shulḥan 'Aruk (vi. 27b, Stettin, 1864), says: "It is forbidden to rob or steal, even a trifle, from either a Jew or Gentile, adult or minor; even if the Gentile grieved the Jew, or even if the matter devolved is not worth a peruta [mite], except a thing that nobody would care about, such as abstracting for use as a toothpick a splinter from a bundle of wood or from a fence. Piety forbids even this."
Rabbi Israel Lipschütz (nineteenth century), in his commentary to the Mishnah, says: "A duty devolves upon us toward our brethren of other nations who recognize the unity of G-d and honor His Scriptures, being observers of the seven precepts of Noah. . . . Not only do these Gentiles protect us, but they are charitably inclined to our poor. To act otherwise toward these Gentiles would be a misappreciation of their kindness. One should say with Joseph: 'How can I do this great wickedness and sin against G-d?'" ("Tif'eret Yisrael" to B. Ḳ. iv. 4).