Sifrei Mitzvot sur L’Exode 34:15

A Ger Toshav -- He who has accepted the Seven Mitzvot of the sons of Noah, as we have explained -- it is prohibited to drink his wine, but it is permitted to derive benefit from it. And one may leave wine with him briefly, but not for a long time. And so too any Gentile who does not worship the stars and the constellations, such as the Ishmaelites, their wine may not be drunk, but one may derive benefit from it. And such instructed all the Geonim. But those who worship the stars and the constellations, one may not derive benefit from their wine.

In the time that the Land of Israel was ruled by the Jewish people, one would purchase wine from other Jews without any doubts. Outside of the land, one would not purchase from anyone unless they had a reputation for upholding the laws of kashrut. Nowadays, in all places wine is not taken from anyone without such a reputation. And so it is with regards to meat, cheese and fish without obvious signs.

One who is a guest in the house of a host, in all places and in all times, and is given wine, meat, cheese or fish - one does not need to investigate further [about the host], even if he is unknown to him, and all he knows is that he is a Jew. If, however, [the host] is reputable for not upholding the laws of kashrut and not applying all its details, it is forbidden to be a guest in his house. And if one nonetheless did come as a guest, one does not eat the meat or drink the wine or trust his word about it, unless another reputable person testifies about it.